Started using sand timers with the 4 yo with regards to getting undressed/dressed and brushing teeth and they have made a massive difference for now.
I got some from Amazon with come in different colours and denominations. For example, using the 5 minute one for him to remove his day clothes and put on his pajamas becomes less of an interpersonal battle and becomes a race against time for him.
I suspect these will be really useful when school starts.
Anyway, I'm probably a little behind the times (heh!), but I just wanted to share my sand timer lurve!