I looked over this guide by Mobiusman https://imgur.com/a/8MFIt

According to it the guide as well as frame data for the game you can only fire a missile once every 9 frames. 9 frames = 150 millisecond [0.150 seconds]. This is a bpm of 400.

If you set a metronome to run at 100, 200, or 400bpm it should be helpful. Again this is something musicians do to train to play their songs at the correct tempo.

Train with the metronome, then after you get in enough practice you'll no longer need the metronome.