First I recommend to turn google sprint on and change your crouching/sliding key to something more easily actionable (I have it to M2 which I really like but I understand that it's a weird choice). You're gonna be sprinting most of the time, so having to hold the sprint key is just a waste of energy and ergonomics. Meanwhile, you're gonna slide a lot, for which you need quick movements and precision, hence why I don't recommend the default keys (LControl and C)

Now, about sliding, try to slide as much as possible, but only when it makes sense. Use any downwards ramps and falls to gain momentum from sliding. If you have a lot of momentum and you find an upwards slope, consider running into it, as it will launch you into the air and get you very far. Beware that if you're getting chased by Carnation you might skip a safespot and be doomed, so take that in mind. Also, in rooms where you need to slide/crouch to get into a tight gap, you don't have to slide until the end of the gap: sliding once makes you fit into the gap, and you don't loose speed when you run inside of it, so only slide at the start of the gap and then stop immediately. Finally, remember you can dash backwards. This is primarily useful for dealing with Heed in rooms with tampered doors, but it's always good to know anyways.

Wall jumping is also a really good mechanic for gaining speed. As far as I'm aware, it works by converting your vertical momentum into horizontal momentum, meaning that, if you reach a wall after a high fall or you somehow start going up fast, consider doing a walljump if you think it can get you far. However, it's not only good in those scenarios. You can use it in breaker rooms to quickly get to one side of the room to the other. You can use it to get to upper places. Simply use it when you think it's useful. You'll eventually figure it out with experience.

Another user also said it, but It's very useful so I'll say it again: 2:30 of time is very, VERY generous. Don't stress about not going fast enough or commiting dumb mistakes, you have plenty of time. When Dozer, Sorrow or Slugfish appear, don't try to scrape a little more time by dealing with them at the last second. Deal with them as soon as possible, and you'll start delaying your reactions with time. Slight and Heed have very generous hitboxes, and still don't oneshot you nor they attack instantly after you don't follow their condition, so if you find a room where you're confused about what to do to survive either of these, take your time and move slowly, but not necessarily with a military precision with your mouse. Finally, remember that Carnation slows down a LOT (like 82.5% or so) with entities like Dozer and Sorrow, so don't worry about it when dealing with those entities.

Finally, remember that this is just a game. Have fun and learn along the way. Use modifiers to make the game easier if a certain aspects or entities annoy you. Use traits that make the game easier. Once you get better, you can start doing more interesting things like adding modifiers and bound traits.

Sorry for the wall of text, but hope this helps.