hi there ,
so you have the BW book "th BW solves all your problems" ? (its yellow)... in that it explains more in depth - not sure how old your little one is but if its a 4 hour easy, it reccomends, that if baby is stall awake, or woken up 90 minutes from the begin of sleep time. (So say wake up is 7, nap is 9 and baby is still awake at 10.30), thhen you should just get your baby up and stick to the same routine in that the baby would be awake for 2.5 hours and next sleep would be at 1pm. a sleep cycle is 45 minutes as you know so its pointless trying once theres only half an hour left to sleep. Also if you wait it out till the correct time - (eg.1pm), the baby learns its sleep times and values these windows.
Hope this helps altough Im not sure if it makes much sense
xxx