I did a laser trigger for my first project.
There's quite a lot to do*, by the time the flash is anywhere near activating all your arduino should be doing is waiting for the trigger.
You should have plenty of time for the trigger to activate the flash and be able to shoot the perfect moment. If not you can extend the distance from the trigger to the arduino, thus giving whatever's moving more time to get to its destination.
When I did it I ended up introducing a delay as the flash was going too early.
*prep the arduino with all the settings, charge the flash, makes sure everything is aligned, check everything, turn the lights out, arm the arduino, open the shutter and drop the object. phew