Hi Val, raising the starting temperature of the epoxy makes it much more reactive and therefore liable to a thermal runaway. In effect, the resin generates heat whilst it cures and in normal circumstances is able to cool itself sufficiently to prevent problems. However, if it is cast in too thick a section; left standing in its mixed state for too long in the mixing pot before being poured; poured in a very warm environment or if it is too warm in the first instance, then it can begin to self-heat, getting hotter and hotter and easily reaching temperatures exceeding 100'C; at which point it will distort, crack and yellow in the very worst circumstances.
To avoid this, I would limit the resin temp. to no more than 30'C and ensure you work quickly to get it mixed and on your part.
I hope this helps