In reply to Cadairmanuk:
I'm afraid it is completely a how long is a piece of string type question!!
I have climbed Tower Ridge in February with barely any snow on it at all, and been on the Ben at the start of May ice climbing...
I think you will often find a lot of snow left on Tower Ridge at the start of April though, and many of the higher ice routes are great at that time (ignoring the last 2 years here).
If you need a definitive answer then my bold prediction is that we are going to have one of the best late seasons for years, with Point 5 being climbed on Star Wars Day. This is based on nothing other than sheer optimism.