Just thought I'd update my own experience of this today. Yesterday (Thursday) at 19:30 I made a booking for a day return flight to VIE leaving this Saturday at 08:05, total cost £98. I knew I had 24hrs to cancel the booking so deadline would be 19:30 this evening (Friday). I changed my destination for BCN and have just booked a day trip for tomorrow instead. I just cancelled my booking for VIE, online, at 11:00 this morning, less than 24hrs before departure, for a full refund.