The simple fact is that training establishments usually have individual fixed leave dates, but...don't assume your phase two training establishment will have the same dates & in all events, if you have a start date to join, it can change and you are still advised to insure against cancellation in case the security status changes which could result in phased leave rather than block leave.
Just to add, for those planning their holidays before they even join...Don't book any outward flights the day you go on leave, nor return flights the day before you're due to rejoin Raleigh. Remember also, you need to inform your Divisional staff to ensure you are contactable during leave (Before anyone thinks "Oh yeah, Really?" - I had a phonecall once telling me to stay on leave an extra week as a course start date had been put back due to illness). The service also gets a bit twitchy if you intend holidaying in countries the FO advise against.