Airline changed my flight time by 4 hours. Can I cancel for a refund?

Usually not. What I’d do:

1. Read the notice carefully. Look at the old and new times and what the airline offers.
2. Check whether the change is “significant”. If it is, you are generally entitled to a refund or rebooking, and the definition depends on the rules where you fly.
3. Ask for a refund in writing if the new time doesn’t work.
4. Don’t just accept a voucher if you prefer cash, since you may have the right to choose.
5. Keep screenshots of the notice and your reply.

Rules differ by country, so check the ones that apply to your route. This flight cancellation policy guide explains the basics.