C41 temperature is critical - to +/- 1 to 1.5C - so is time...

You can overdevelop a little - all you get is an increase in dye build up and a bit of a color shift..

If you were 2C under temp and developed for the normal time you should still have gotten negatives that were printable - not easy, but printable..

I used to process C41 (and C22) comercially - have done it in deep tanks, dip/dunk, jobo and auto processors...

The trick is try to keep the temperatures of all baths within a couple of degrees of each other..and keep your time consistant...