I have began to learn that booking flights and car hire early does generally provide very good savings. This year I have been bitten twice by booking early with Ryanair.
I have booked two return flights so far this year, both have been re-scheduled by atleast 12-14 hours. On the one occasion I couldn t accept the alternative flight that same day so was forced to take a flight two days later. Ryanair are great for offering you an alternative flight no matter what the cost, mine was twice the price in the end. The car hire price however had increased by over £100, a cost which I had to foot the bill for.
Not much you can do about this situation, but worth considering when you book car hire.