Don't leave before everyone else does. Of course, reach on time.
Figure out the routine of your colleagues and try to gauge what's acceptable and what's not.
Most importantly, ask a lot of questions to either your colleagues or your boss, could be about the code, the product or any other thing.
Keep a tab on pull requests/code merges being made right from the first day, even if you don't understand them, glance through them. Code bases are complex, so you can start asking about how to understand the coding style.
If you're provided with a machine, try to set up the dev environment right on day 1. You can focus on code from day 2 and try to ship something small within the first weekend. Good luck!