When laminating it is ideal to have the resin in the PVA bag just long enough to get it down to the trim lines before it begins to cure. If it is poured immediately after mixing it will be filled with air bubbles which may lead to starvation. If the resin sits in the PVA bag for too long it may start to dissolve the bag which can result in starvation. Also, ensuring the resin doesn't go too far past the trim lines means that it is less likely to clog up the vacuum stations, and will need less resin overall to complete the lamination.
Knowing when to pour the resin is better than just adding extra catalyst as it is wasteful and may cause the laminate to get too hot. To know when to begin to pour requires a bit of practice. When laminating, time the resin from when the catalyst has been added until it begins to solidify. Make note of the time it took, the materials in the lay up, the type of resin, any pigments or dyes, and the relative temperature of the cast and room. Factors like a carbon fiber lay up, a warm cast, a hot day in the lab or different combinations of pigments and dyes may decrease the working time.
Once an estimate how long the resin will remain workable is achieved the next step is knowing how much time is needed for the resin to reach the trim lines. A short trans tibial socket may only require 3 minutes of work, while a Symes may require 10 minutes. The thickness and strength of the vacuum will also influence the speed the laminate will travel. A thick lay up or weak vacuum will mean that the resin will impregnate the materials slower than a thin lay up with strong vacuum.
Note how long or short the cast was, how thick the lay up was and how long it took to reach the trim lines.
This information will give a baseline to judge the timing of next lamination.
Total Resin Working Time - Time To Reach Trim Lines = Time To Let Resin Sit
Please remember to let the resin sit in the fume hood before pouring and that pooling resin will also cure quicker (i.e.. reservoir)