This is probably a dumb question, but I'm trying out speedrunning for the first time and I can't figure out how people sync up their splitting software to the game.

Right now I'm using LiveSplit, and tried setting up a mouse button shortcut to start/split the timer, but it feels wrong because it depends on me hitting the button at the right time. Is there a better way?

Split is not a big issue. The important thing is the start and end. For example, by making the time negative at the start, you can start at the moment when the time reaches zero. I recommend setting shortcuts on the keyboard rather than the mouse.

As mentioned by toraji, the most important ones are the start and the end. The timers start the sec you have freedom to move from the drop pod and ends the second the pull handle reaches the bottom and locks. The splits all depend on how you put together your run. Your run might be slightly different than someone else’s run so your splits might be different. I also recommend a shortcut on your keyboard. I use the enter key as my shortcut. It’s very easy to hit with my right hand that holds the mouse.