You guys need to read the package:
Permatex recommends immediate assembly, specifically stating "Assemble parts immediately while silicone is still wet." None state to leave open for any period of time or allow them to "skin".
Depending on the product they recommend different processes:
for HI-Temp, Sensor-Safe Blue, Ultra Black, Ultra Blue RTV Silicone Gasket;
Finger tighten flange only until material begins to seep
out the sides of the flange.
Allow to set for at least two hours and re-torque at
lease one quarter to one half turn.
For best results, allow to cure overnight
for Ultra Copper RTV Silicone Gasket and Ultra Grey Gasket Maker;
Assemble parts immediately while silicone is still wet.
Secure or tighten to recommended torque specs.
Re-torque will not be necessary after the product has
cured.
Right Stuff has slightly different instructions;
Assemble parts within 5 minutes while The Right Stuff
is still wet. Secure or tighten to recommended torque
specs.
Re-torque will not be necessary after the product has
cured.
http://www.permatex.com/products/Automotive/automotive_gasketing/gasket_makers.htm
They claim the right stuff has no cure time and can be put into service immediately.