Why is my epoxy curing so slowly?

It seemed my epoxy was curing rather slowly. I thought this was good because everyone is always telling me not to let it get away from me. But today I thickend some up to fair in some little bubbles and it just wasn't kicking off. That's when I read on the can of slow hardner that it is only recommended down to 60F and the temp in the shop was at 50F. So I went to Anacortes to get the "fast" hardner that is good to 40F which should work fine except for the coldest days this winter. No one had it in the"C" size so had to drive up to Bellingham and found some at LFS.