Since it takes 2-3 seconds for me to load a Geometry Dash level after pressing play, can I start the timer 1-2 seconds after I pressed play? And if yes, can I pause the timer for 1-2 seconds when pressing play on a second, third or whatever level? Because it's not really fair that people with a Gaming PC can load a level under 1 second, and I, a laptop player, has to wait 2-3 seconds.

Then the timing isn’t done by RTA, so no you can’t. I understand it isn’t really fair but that’s how it is.