They won't die without circulation for 1 hour. Just worry about your fish. Anyway, you don't need such a long time for epoxy to cure. Normally it only takes a few minutes before you can on your circulation again. If you can remove the rock you want to epoxy the sps to, it would be good as it cures better out of water. Simply epoxy it out of water and leave it for around 10 minutes. By then the epoxy should have taken hold and you can place the rock+sps back into the tank. If you are talking about epoxying it underwater, you have to use alot of epoxy and most likely you will have to hold it in place until it takes hold. So most likely you'll be holding the sps underwater for a few minutes at least. IMO it is easier to epoxy it out of water. Smaller colonies or frags can be epoxied underwater quite easily. Superglue gel works just as well.