How important is temperature when adding pectic enzyme?

The optimal temperature for Pectic Enzyme (Pectinase) is about 45 degrees Celsius. Any temperature above that will decrease the rate of enzyme action because the enzyme will become denatured.

It is best added when the must is at room temperature, you don't say what temp it was added so to be on the safe side I would add another dose. A double dose won't harm the resulting wine.

I'm making plum wine right now and was wondering about this. While this may not be an official "answer" here, I have read that you can pretty much add pectic enzyme at any point in the process, but it's supposedly best to add it in the beginning. Pectic enzyme effectively un-does the work pectin does in your wine-- pectin wants to make it into a gel, but you want a clear wine in the end. Pectic enzyme works to shorten the molecular chains that pectin forms in your must and wine-- while most fruit doesn't have enough pectin to make a gel on its own, those chains cause haze later.

My experience making wine tells me that if you're aging your wine in oak or in a carboy with oak chips for at least a few months, you can add the enzyme powder whenever you want and it'll do its work over time, similar to the way malolactic bacteria work on your wine once its in oak to covert malic acid into lactic. I'm pitching yeast tonight after a day long fruit rest and don't have any pectic enzyme on-hand, so I'm going to add it midway through fermentation and will report back on how it goes.