Transition Time from One Task to Another

My son who has Down Syndrome attends a mainstream preschool. His teachers mentioned that it takes some time to transition from one task to the next. What tips/advice can we give the teachers to help my son shorten the transition time? Thanks!

Is it because it takes him time to get there or time to put away stuff? Maybe using a timer to help with one task ending and the other beginning or give him a slight ‘head start’? Just brainstorming a little!