I can only offer some advice...
Hmmm... I don't think saving and going at it again works. I never tried that, though. I don't know if you've tried this, but it worked miracles for me. TURN DOWN THE VOLUME! Hit "mute" or something... When I got rid of the distraction of sound, I realized that I timed things very well. The sound of thunder is sometimes inconsistant with the way things are timed, so it's better to focus on the flash itself than the sound. See if that helps. If you have tried it, that's all I got. Hope I helped!
~Glitch