Concentration and writing

If you pick up any guide to effective study, or self-help book that professes to teach creativity you'll find the same message. Humans can't concentrate for more than 25 minutes at a time, therefore, we should not read, write, revise or otherwise engage in strenuous mental effort for more than about half an hour.

Yet we all know and believe that creativity comes in a white hot passion that consumed the creator and leaves him or her working in a frenzy into the small hours, doing without sleep and food ...

So how to reconcile these two statements?
I think that for most of us, the 25 minute rule just doesn't work, because

(a) we can't settle in less than about 20 minutes, so we need to set 25 minutes from when we actually begin to concentrate and/or create, not just an arbitrary clock period

(b) while it may be true that our best work is done in those 25 minutes, our emotional and spiritual satisfaction comes from long and intense engagement with our creativity, so the work may not be as good but the personal rewards are greater.

Do I have an answer to the conundrum?

No - but I do keep a timer on my desk and try to take a five minute break every thirty minutes. Often I just cancel the timer and work on because things are going so well, but sometimes I get up and do some exercise or wander round the garden. I don't stop thinking about my work, I just give my body a break and I do, really, truly, think it helps ...