At the end of reception your child should have a basic understanding of time. They should know the day divided into morning, afternoon and evening. They will also be introduced to a sand timer to help them taking turns, so they will get quite good at estimating how long is 5 minutes. I use a sand timers probably too often, but it keeps my son on task. For example I give him 5min to put his PJs on. Evil, yes, I know.