[SOLVED]How do I set the flash duration to while a key is down?

I'm trying to make a muzzle flash in my spaceship bullet hell game and I can't seem to get a muzzle flash working. Initially, I just toggled visibility with a system wait in between but I had very poor results so I thought using flash would work better but I don't know what to put for the duration.

I want to be able to hold space and spam out bullets with muzzle flashes.

You can use a Timer that toggles visibility, and just have it start and stop based on input, with the added step of making the muzzle flash invisible, just to make sure, when you stop.