As mine gets older, I increase the amount of hardener.You guys have had much better luck keeping 10110 Devcon than I have.
My last two large containers both started experiencing extended cure times before the expiration date passed. New container=hard overnight. 8 months later, and I've got a space heater running on the rifle to get it to cure in a reasonable amount of time.
Yes, I was weighing it on a scale. It wasn't a one time deal either. I'm just storing it in my shop, which is climate controlled all year. Maybe keeping it cold would help, but I'd at least expect it to perform up to specs until the expiration date arrives. I emailed Devcon and they pretty much just said that's normal.