In Darkman II, Peyton learns how to extend the 'life' of the synthetic skin from 99 minutes to over 150 minutes. This technology, while apparently so simple Peyton is surprised he never thought of it in the previous film, is never seen again.
At around 16 minutes, when Peyton checks the cell integrity in the mask after his timer reaches 99 minutes, the timer overlay in the microscope view reads 98 minutes.
The car that drives by Darkman coming up through the manhole around 1:13 does not have their headlights on, even though they are driving in the dark. (Note no taillights on at all.)
As the thugs fire down on Darkman running across barrels of (apparently) explosive chemicals, the barrels are clearly being detonated from underneath instead of inside. Firing into a metal barrel filled with explosives would explode out, not straight up.
Dr. Thorne is (or at least claims to be) one of the doctors who cut off Peyton's pain receptors, leading to his enhanced strength. Yet, despite familiarity with this technique and its side effects (familiar enough to reverse it), she cannot duplicate the altered adrenaline in Rooker's thugs simply by performing the procedure on them (or at least some poor sap they don't have to hunt down first).