Booking a holiday right after exam period

I am going to book a holiday in late May to celebrate the end of my bachelor’s degree. However, it will take me until late March to know the exact dates of my finals, and hotel prices will be higher as I get closer to the date of travel.

There is one thing I know, is that the final exams will last no later than 29th May. This will condense my 4 or 5 day trip to a 3 day trip (30 May to 1 June).
Can I take the risk or higher costs of hotels to go before the official end of exam period? I will have a refundable booking which starts 30 May just in case, with the flight departing at 1:50 am that day.

You haven't explained why you can't just plan to start the trip on 30th May and finish on, say, 6th June. Why does the trip need to end on 1st June?
If the booking is fully refundable, then you can go ahead and make whatever booking you like, knowing that you'll get your money back if it ends up clashing with your finals.

I have an important camp to attend on 2-4 June

And after 4th June?
As I said above, you can certainly take the risk of booking something - knowing that you can get a full refund if necessary. But if you do find that there's a clash with an exam and so have to reschedule your holiday, the cost of everything may well have changed.

I found a really great set of dates now.
My camp on 4th June ends just before lunch, which gives me enough time to head to the airport to catch the 4:30 pm flight that day. I can return on one of the two evening flights on 7th June.

I am now looking at the dates of 5-14 June, as I have something scheduled from 15-25 June. There is no risk of clashing with any exams!