I have limited experience doing it. But I did it for a few years in a row a while back in northish Idaho with a buddy who owns some property over there. He would start the baits end of April with at least one fill up, and then really juice them up once we got there around Mother’s Day. We would take multiple bears every trip of of two different barrels.
I’d say starting sooner is better. As the green up happens, bears disperse, more food sources available, snow melts, I think the less effective the baits are.
I’m over here now spot and stalk bear hunting. Seen two over the week. It’s hot. Killing time during mid day. Both weren’t out until 730 pm.