'Time is of the essence' is a phrase you would use to describe a situation when you are in a hurry and you want someone to act straight away.
It's rather an old fashioned way of talking though, and you wouldn't really use it in everyday chat. It could be used formally, say by lawyers of doctors, to describe immediacy. E.g We should proceed with the operation tomorrow - Time is of the essence!
It's the kind of thing I say when I want to be a bit dramatic! I will use it with my grandchildren to emphasise what I'm saying. So I'll say, "Come along now, make haste - time is of the essence!"
Interesting they never say, "What does that mean Granny?" They know what I mean by my body language, my attitude and the fact that I'm shepherding them out of the door at the same time. They just look at each other and roll their eyes - Grannies!!
