How to speed up flash powder flaming reaction
First, we postulate safety is not an issue. If you try any of this you will probably die.  If you need a short duration event-triggered flash, explode a wire.  A Pockels cell plus a polarizer is a nanoseconds shutter.

Ball mill potassium perchlorate all by itself.  Mix well with micronized aluminum.  Compact.  (Impact, friction, or a static discharge may kill you.)

Aluminum has a high boiling point, 2519 C.  Magnesium is 1091 C and burns under nitrogen.  As above, with micronized Mg, adjusting stoichiometry for the new equivalent weight.  Same warning.

Use a more potent oxophile, like titanium, adjusting stoichiometry for the new equivalent weight.  Micronized titanium can flash in air, nitrogen, or carbon dioxide all by itself.  Same warning.

DO NOT TRY CHLORATE, as opposed to perchlorate.  There is almost no activation energy barrier to reaction.