Keep in mind there is no “general rule” about how fast FP go away, as this is related to how many FP are delivered, every day, for an attraction, which is something that might change from one day to another, depending on the expected attendance.
However, I would say that most “e-tickets” ride do not run out until mid-afternoon. Obviously, if you're staying on a short trip, you might not have FP for all the attractions you'd like, as you cannot have more than one FP at any time, for one park (except exceptions). I would also suggest that you rope drop some rides if you can!