It depends on the session and there's no right answer, it's subjective but here's an attempt at explaining: You will be able to do higher volume (more sets and reps) by taking 60-90 seconds rest. This means more micro damage to your muscles (which we want) which means once you fully recover your scores should be higher and you will find the individual exercises easier. Most strength athletes bodybuilders etc take 2 mins or more rest between sets. HOWEVER From memory a lot (pretty much all) of the phys at Lympstone is intense, back to back, determination stuff. IMF and Bottom Field both absolutely gas you out. So you need to condition your body to be used to this. If you're constantly taking loads of rest you won't build up that engine to deal with the lactic acid and pain, or the cardio side, so you'll struggle and life will be harder. HOWEVER (again) If you smash yourself to within an inch of your life every day you will burn out much faster. You won't recover as easily, your scores won't be as high, you might get sick or injured. Even the big military fitness experts online like Sean Lerwill (ex RM PTI), Simon Jeffries (ex SBS) and Mike Chadwick (Para PTI) just recently spoke about training smart and not making every session too intense. So Find the balance. I'm quite happy with my scores (max on press-ups and sit-ups, near max pull-ups, decent 1.5 and bleep) and my overall conditioning too, there's always work to be done but I'm happy enough. I try to do 2x really hard continuous circuits each week (not including the VPJFT which I'll do as a warm up for strength sessions), then on strength days with the weights I'll take 45-60 secs rest between each set. Sometimes if you feel there's "more to give" then you can always do some Tabatas or HIIT stuff for 10 mins at the end of your slower sessions as a "finisher". Then just make sure you get enough rest. Honestly over time I've found MORE fitness gains from 3-4 strength & conditioning sessions each week rather than smashing out 5-6 where you're never fully recovered.