When I have tried to release the parts while hot it works but I always feel the parts seem difficult to pull and release. Letting them self release with the cooling/shrinking works well.

The problem is when you have a multi section mould that has zero draft or has sections that are on 3 or 4 faces so if the mould shrinks it actually gets tighter round the part and it cannot self release.. The dive bottle cover is one part where there is zero draft and it locks in so tight that the best way is to actually ramp UP the temperature 10 degrees just before you remove the part! The fuel tank moulds also get clamped down upon when the mould cools and as it is 4 or 5 sections the time it takes to remove all the sections is too long to remove it all before it starts to shrink.  In both cases the moulds crack. I have done a few parts from one piece moulds that will self release when they cool. Great when it happens but almost all of mine will not self release so wet lay tooling shrinking is my worst nightmare.