+xYes, resin will tend to 'go off' much quicker than gel coats and temperatures above 20 degrees will accelerate things quite a lot
Be wary that some catalysts will be formulated to be fast acting also and designed to work better in cooler conditions
If you can't control the ambient temperature, then working with smaller batches of resin can help to try and avoid things hardening before you've had time to apply
Can't put less catalyst? That won't slow things down?