It's pretty standard for polyester and vinyl ester based resins to be measured in 150g mass at 2% catalyst and 23 degrees ambient. Target gel time is normally 20 minutes.
Rough rule of thumb is that every 5 degrees above that will halve your pot life. So 28 degrees at 2% would be closer to 10 minute pot life. Then the amount you mix affects things, as well as the type of container you are using (ie. Tall skinny cup goes off faster than a short wide cup).