As others have said it's best to stay with them until they wee/poo, otherwise you don't get chance to reward them for it.
And the longer you are outside if they don't, the more chance there is of them being due to go if you go back in.

Bloody boring though isn't it!

And try not to get too disheartened by setbacks, we thought we had our puppy cracked (optimistic after only a week I know) but yesterday morning she has peed on the floor before we had managed to get a door open, peed again while this was being cleaned up, then while I was looking for the keys she was 'curling one out' in the corner. This became the order of the day and it was as if we had gone back to square one but with more time outside and better vigilance we are back to some sort of routine.