What does the timer need to start on? I tried -2.70 but my splits seem inaccurate. Also, is there something on livesplit to round my splits to the framerule if I miss a split by a few milliseconds? because this also happens quite often.

If you mash start to start on the first framerule after resetting the game, then it would be -3.27 from the point of the reset (or from selecting the game, if using a multi-game cartridge). Starting the timer from the start press will be inaccurate because of framerules—the game can only start every 21 frames which means that the time between pressing start and the start of the run can vary by up to 20 frames depending on exactly when you push start (it'll be anywhere between -2.59 and -2.92). So, I don't recommend starting the timer that way.

If you're playing on emulator (FCEUX, Nestopia, or Mesen), you may consider enabling the autosplitter from the Edit Splits window. Then the timer will automatically start and split for you, so you don't have to worry about it.

Thanks