I've decided to recommend from A03 just becuase I'm sure you all are so familiar with the FFT Archives. My favorite trope, without a doubt, is Time Travel, so here are my favs:

1. Time Mutable Immutable by deGroot- It's a SS/HG. (I know a lot shy away from that pairing) but I love them together. Hermione is trying to stop some Voldemort Worshipers from changing time. They have determined that Snape is the lynchpin to the entire war and she must protect a teenage Snape. I love the friends to lovers slow burn as she realized how easily she could fall for him when he grows up, but the best part is the end when you realize why she was sent back to begin with. 

2. Butterfly Effect  by Nicolvr11 - Unforunately, this one isn't complete but it's still 242,000 words so plenty of story to enjoy. In this AU, Hermione goes on vacation with her family over the summer between 2nd and 3rd year and ends up stranded on a semi-deserted island (with a diabolical wizard doing human experimentation on it.) She finally escapes and returns to the wizarding world to discover that everything is in shambles, Voldemort is in control and Harry is dead. (Because we all know Harry wouldn't have made it through any of the books without Hermione.)  She then goes back in time to the third book to change everything. The author jumps between young Hermione on the Island and older Hermione at Hogwarts as she enlists Sirius, Remus and eventually Snape to help her change the world. It's truly addicting and I hope the author finishes it someday.

3. The Way of Conquest by pagination  This one is crack treated seriously, but it's hilarious and makes you realize how stupid characters can be. The Mandalorian gets pulled back in time (Some force osik) and lands directly on Chancellor Palpatine just as he is voted in for emergency powers, accidently killing him, thus making him the new chancellor. Mando and Grogu have to naviage this strange new world, dealing with lots of stupid political decisions. (A full frontal assult to extract three people who were trespassing and spying. Are you trying to start a war?) all while not realizing they are in the past. (Hey, Alderaan, you got a new planet. Probably should have picked a different name though.)  It's well thoughout and hilarious.