A few things to try.
Bait less, they soon learn if they don't show up quick they get nothing.
Bait with sweets, something they can't get anywhere else. Blackies are suckers for sweets. Stale donuts, popcorn with syrup or similar.
Bait at the same time every day.
Make noise, the same noise everytime you bait. They get conditioned to noise = food. Don't sneak in to bait, you don't want to surprise them on the bait.
Are you using and can you use a barrel? If so you want the opening just big enough to get a paw in to pull out bait. Makes them work harder, stay longer, and make more noise that attracts other bears.