In reply to Paul Sagar:
Putting aside the HIIT topic for a moment, if you're really trying to specialise Ancap I'd suggest increasing the difficulty, reducing the work time and increasing the rest time between boulders.
Adapting your current session, this would take the following form:
Define three 6-8 move problems which are a little harder than flash grade, and pre-practice so you have them wired.
Complete one lap of each boulder with a 60 second rest between each lap.
Complete 6 sets of 3 laps, resting 3 minutes between sets. You should find yourself failing on the last lap of the 4-6th sets.
If you complete all the reps, increase the difficulty next session either by defining new boulders, or by adding 1-2KG with a weight vest. Don't add more than around 4KG with the vest as it will start to negatively affect your movement efficiency.
I've found this session to be very effective for improving ancap. What you're currently doing sounds more like aeropow which is great for sharpening up your route climbing power endurance but won't lead to good gains in ancap because the aerobic element is too high. 90 seconds of work is too much for ancap which should peak out around 45s of continuous work IMO, ideally a bit less.
For aeropow though I'd recommend ideally a bit less rest and a little more work. My favourite for this is 4x4x4.
This comprises the following:
4 boulders, 2 grades below flash, 5-7 moves. Complete one lap of each boulder with no rest between, just a quick chalk up and back on the wall.
Complete 4 sets of 4 reps, resting one minute between sets.
Complete the above workload 4 times to make for 4 super-sets hence 4x4x4. Rest 4 minutes between super-sets. You'll do approximately 64 reps and feel VERY pumped! Works like a charm though. Also great for conditioning skin for big days on the rock.
Hope this helps.