Once had a manager repeatedly tell me I needed to "manage my time better" when I told them I didn't have enough time in the day to get all my tasks done. So I logged my time one day (9-11 worked on task A, 11-1230 worked on task B, etc.) and went to my manager to show them. "This is how long I am spending on each task, can you tell me which ones I am spending too long on and how I can be more efficient?" Manager told me to give them the log and they'll get back to me.
They never did get back to me, but they did end up reassigning my duties to other people who were also not given enough time to complete them.