Time-loops can be quite long
Sirius Black rushed in his form as Padfood through the halls of Hogwarts. He could smell the rat and was closing in. This time he would get the traitor. One more corner and the rat was trapped. Sirius transformed raising his wand and stunned the rat. Now he could trap it and then force him to transform. He wanted to see the look in Peter's face when he would get what was his due.
He just started the spell to force the transformation when he heard an audible gasp and then a girl starting to scream and run. He had to silence that little whelp he was so close. He send a stunner after her but she vanished behind a corner. So he chased her turned around the corner. The girl with the bushy brown mop wasn't the fastest on her small legs and began to panic looking behind her wasn't exactly smart and she tripped. His Petrificus Totalus hit her in the exactly wrong moment sending the poor girl falling to the floor and crashing into a wall. He had no time to even think about whether he should help her or get the rat first when she vanished in a cloud of golden dust. Since someone might have heard the struggle he decided to get the stunned Peter and run only to find himself looking into a raised want when he turned around. The small old Witch pointing his wand at him spoke to him:
"Well Mr. Black. It seems the three of us" she was held up the rat on his tail in her other hand "will now have a conversation what two animagus are doing rummaging in my school." before he could answer his world turned Black.
Harry and Ron became quite agitated. No one had seen Hermione for a while. She was neither in the library and even missed some of her classes. If she wasn't showing for dinner they would have to go to Professor Mcgonagall. Neither of the boys was eager of a repeat of the troll fiasco, or of finding Hermione in a petrified state. Before they could approach the head table though the large doors slammed open and an old whitehaired witch marched determinately through the hall towards the head table. In a flash of light Dumbledore's throne was pushed to the left and shrunk into a normal chair and a new chair appeared in the middle of the table. The witch approached the lectern and spoke:
Every student and teacher suddenly felt a strong compulsion to comply
"Hereby I Helga Hufflepuff invoke the Founder's claim and retake control of the school. For now the school will run as you are used to it but expect important announcements about necessary changes in about one or two weeks."
She turned to Albus Dumbledore.
"Headmaster do you recognise my claim as stated in the school's founding charter and as you swore when taking office?"
Dumbledore rose and bowed to the old witch he responded:
"This is a joyous day. Finally you returned as foretold and finally we will be free to tell the true history of Hogwarts and it's founders again."
Little by little student were able to overcome the compulsion to be silent while this happened but the confirmation that the actual Helga Hufflepuff was standing in front of them was the breaking point. The murmurs from students talking to each other or shouting questions grew to loud to understand anything. So the witch drew her wand and with a simple flick no sound could be heard. She looked at Harry and Ron who still stood half way towards the head table.
"Mr. Potter, Mr. Weasley I assume you want to inform a teacher about your inability to find Miss Granger?"
Given their inability to produce sounds both boys simply nodded.
"Then let me ease your worries. Miss Granger is safe and sound. I'm afraid I can't offer you more in such a public manner and I have pressing matters to attend to for the next day or two. So if it would be agreeable to you I would like to meet you in my office Friday after classes."
Albeit not really happy both boys could only nod.
The witch turned to Albus again.
"Let's have dinner. Afterwards I want to meet the staff in the staffroom and then the two of us will need to talk in private."
The next three days were a hectic affair. Next to the education staff only some researchers and scholars worked at and or visited Hogwarts. But now politicians, Aurors and all kinds of other people were coming and going. Meanwhile there was no sight of Hermione. Harry and Ron even used the cloak to sneak into the Infirmary and then remembered the map but no sign of their friend. Rumors were flying around and the Daily Prophet printed theories. Those ranged from the witch being an imposter, to her only being the first of the founders returning after staying in magical sleep.
Thursday's headline saw the Ministry officially acknowledging the witch as Helga Hufflepuff citing her delivering pre-defined proof to confirm her identity after her foretold reappearance. There was also an announcement that an official procedure will take place on Saturday at noon and that attendance was mandatory and each student will have to attend in full formal uniform (including the much hated pointy hat).
Friday after classes Professor Mcgonagall escorted the two boys to the Headmaster's office. Albus Dumbledore was sitting in a chair in front of his old desk and Helga Hufflepuff where he usually sat.
"Hello Mister Weasley, Mister Potter, I think I still owe you an explanation about what happened and the current state of your friend Miss Granger. Well it all started with Miss Granger wanting to take all elective classes …"
The boys were informed their friend had a time turner all along. That when she was chased by Sirius Black this time turner broke and the time sand reacted unexpectedly likely to a combination of the ambient magic of the castle, Sirius Black's active magic and Hermione's magic reaching out in her panic. Their friend was send back in time more than thousand years. Harry looked at the legendary witch:
"Did you meet her? Can we bring her back? Or did she at least have a good live in the past?"
The old witch smiled at him while she responded.
"Well I think my life turned out well so far Harry. But it is not over yet."
Both boys just sat there with their mouth hung open. They looked at Dumbledore whose eyes were just twinkling as he smiled and addressed the boys:
"I can't express how much it pleases me to finally meet some people again whose friends are older than mine."
"Bloddy hell. She knows us inside out we'll never get away with anything ever again!"
Mcgonagall just had her usual thin smile to show that she was quite amused at how this played out.
For now just a one shot. But one of the more frequent ideas in my head.
I get bored with yet the next time travel to:
a) Any of the Schoolyears
b) Mauraders time
c) Tom Riddle (either Schooltime or as child)
Founders is sometimes done but usually not in an interesting manner. Usually it's just a train up fic. Should I expand the story I might touch on why assuming old magic is better magic is kind of stupid (that would not only mean there is no spell development taking place but it also is defeated by people ~1000 AD not having concepts of many things we assume as normal day to day stuff in the modern age).
I have some plans should I find the time to expand this idea. I.e. a thousand years is a lot of time. So what everyone knows about the founders is unlikely to be the true story. Hermione will certainly set them straight. While she was not able to interfere she could plan for her return and on top she is one of the legendary founders so she has a lot of sway.
Should you like the idea of a long time-loop with someone turning out to be one of the founders go ahead and run with it. Would love people fleshing it out better than I can.
Reasons I picked Hermione:
a) She had the time turner in year 3
b) Her thirst for knowledge combined with they don't change what you know will happen turns her own nature into some kind of a curse for her.
Rather than Harry (overused and destiny in his own time) Ron might have been a good alternative pick finding and playing with Hermione's time turner. He of course would have turned out to be Salazar Slytherin and not amused how his historic image was twisted beyond recognition. ´