Bondo/body-filler working time (On Topic actually)

I tried using Bondo to make fillets and repair defects in some patterns that I am making to cast. For this kind of fussy fiddling, the Bondo
sets up much too fast (3-4 minutes). Is there some way to increase the pot life/working time? If I use less hardener, will that slow it, or just screw it up? Is there something that I can add?
TIA, Bob
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