When should I add the internal mold release to the resin mixture?

Order of addition is another important consideration.

If the order of addition has already been established using an existing internal mold release, using the same order is a sensible starting point.

If this is a completely new program, it is generally advisable to add the internal mold release before the initiator/catalyst and before the addition of fillers and pigments. This ensures sufficient absorption of the internal mold release into the resin.