Wouldn't it be better if the time started as soon as you press the play button so you don't have to start the timer with -something?

It's better to start the timer when the first level is loaded because the time is more relevant.

You can change the hotkeys in your LiveSplit settings (right click on the timer then "Settings") if you space bar is not working anymore.

Or you can start your timer when you press the play button but your run will be retimed with the timing rules.