I've run into the slow setting epoxy also. A couple tricks for cold shop use. First mix more than you need, a small amount for some reason doesn't want to set as quickly even though you use the same amount on the joint. The other thing is to use a couple 100W bulbs e 6 to 8 inches above the piece to speed the cure. Sometimes, the stuff just is slow to kick off and I've had it go two or more days before it was cured. I've never noticed any weakness in these slow cure joints though.

Don