iwearflairs - timers can work well. I take a 5 min sandglass one to the park, and use it to help announce when it is time to leave the park. The boys are warned at 10 mins, 7mins, then timer is produced at 5 mins, which they can then view (if they so wish), and I will announce when there is about 3 mins left, 2 mins left 1 min left. Get some odd stares from parents in the park, but it does seem to work as a way of letting the boys know the timescale in which I expect them to comply.
Undesirable behaviour (hiding under a bed when it is bedtime for example) can be counted using the 1-2-3 method, but I try to avoid using this for what is known as start behaviour (such as starting the bedtime routine).
Delay tactics I find often includes not wearing clothes (children seem to learn quickly that if they are naked, you won't take them out of the house). I use the timer for this (getting dressed is 'start behaviour') by saying "If you are not dressed when the sand runs out, I will get you dressed." When they start making an effort to get dressed (to beat the timer) I then offer them assistance. If they refuse to get dressed, the sand runs out, and I get them dressed (you know that battle I'm sure).
I find it's give them a simple choice, and hope that they make the right choice. If they don't, then carry out whatever the alternative choice was.
But the worst thing is that he won't stop any game he is playing in the middle, e.g. to come and eat lunch while the food is still hot.
I wouldn't want to stop doing something I was enjoying either! If they are enjoying something, why disrupt it. Food can often be kept warm (or eaten cold).
Advance Planning can help with this type of situation... a set meal time for example. Also prior warnings that the meal time is approaching, and it will be tidy-up time. Warnings at least at 10 min, 5 min, 3 min.
Using timer from 5 mins to countdown the remaining time to tidy-up time.
Bedtime tip: don't insist on sleep. Insist that they stay in their room. Always try to follow the same wind-down routine, so there is plenty of advance notice that bedtime is approaching. Drink of Warm Milk with an oat biscuit can help (both contain Tryptophan an essential amino acid, which has been found to be an effective sleep aid).