Progressing in static holds

So right now I'm working on two of the bigger milestones of F1, which also happen to be two of the toughest static holds: HBH and RC/PE6.

I've just reached 5x60s in HBH with as by my sides and I'm currently working on 4x48s in the chin holds. Progress so far has been slow (especially on the first one) but still progress.

The approach that I'm using is to take some rest between sets (30s/90s at the most ) to get to 5x60s and then work on reducing the rest time. But now I'm wondering if this approach even makes sense in the first place because I'm afraid I'll stall for a long time once reached 5x60s.

So my question for you guys is: have you tried this approach with success before? Do you suggest me to scale back but have no rest time instead?

Thanks for your precious time

THis approach is not suitable for beginner. the reason basically it that the intensity must be increased gradually. 

Lower intensity and progressively increase it or volume does not stress in the same way as full intensity and decrease the rest.

the way you chosen could be used by advanced athletes to build up endurance when you can hold easily basic work. 5x60 sec is basic work.

That makes a lot of sense. I'm going to implement this approach from my next workout. Hopefully I won't see too much of a drop in my holds

Grazie mille Alessandro!