We booked a holiday for June next year about three months ago. We booked with a company who we don’t normally travel with as they had the best flight times.
We are flying to antalya and normally the flights are late in the evening. The flight we booked was scheduled to depart at 6am. We were planning on going anyway but it just so happened that a friend of ours who lives in turkey was having a birthday party that evening and this was the only flight which worked for us in that regard.
We have now received notification that our flight has been changed by 11:40 to 17:40.
The tour operator’s definition of a major change is more than 12 hours. 
I’m so annoyed about this and I’m at a bit of a loss as to what to do. How can a change of almost 11 hours be minor?