From what I can tell, problems tend to arise in three main time bands - 8-9, 12-1 and 5-6. It's rush hour in Marple!
Little more seriously, in my experience it's delays turning right into Stockport Road. You turn right then pretty much always get immediately hit by a red light at the junction of Hollins Lane. If that red light has backed up with traffic from Stockport Road, it's difficult for drivers to get out of Hibbert Lane, so backing up starts. And once it starts, it gets worse and worse.
What's the solution? Changing the Hollins Lane traffic lights to favour Hibbert Lane drivers would just cause backing up on Stockport Road.