Roger. FWIW..... It all depends on the rising versus falling edge characteristics of the output AND the surrounding circuits. Photocells will tend to always turn on very quickly and sharply. The turn-off can be lazy and unpredictable, or it can be sharp; that depends on the loading that the circuit that is being driven presents to the photocell. If it is a heavy load, then it will quickly drain the residual charge out of the middle ('intrinsic') portion of the photocell semiconductor junction and the turn-off will be quick and sharp. If lightly loaded, the turn-off will be lazy. So if you somehow reversed the leads and could trigger off of a lazy photocell turn-off edge, it would be unpredictable......just like the Mopar's Hall effect sensor. As said...FWIW.. just a possibility for the OP's timing changes with hot temps.
