My reading of UK/EC261 is that a significant retiming is treated as a cancellation. That means bringing the flight forward more than an hour, or delayed arrival which I think is 3 hours. This ought to be independent of the 2 week window which is used to gate compensation. I'm going to ask this question in the appropriate thread as I really don't know the answer.

30 minutes? No chance. That's really a noise level delay, like having a delay of 30 minutes getting to the airport, it just eats the safety buffer you should have built in to the plan.