Question - R.E.M sleep and WBTB

Each sleep cycle lasts approximately 90 minutes with the last stage of each cycle being REM sleep. This REM stage gets longer as the night progresses. With this information one should be able to get longer and more frequent LDs, in theory anyway, by calculating the exact time to go to bed and wake up.

So lets say you go to sleep at 11PM with the intention of doing WBTB. You wake up five hours later at 4AM which would be roughly 1/3 into your 4th sleep cycle. So here's the question. If you stay up for an hour then go back to sleep at 5AM, where are you in your sleep cycle? IOW, does staying awake for an hour reset your sleep cycles or would you be where you would have been had you not woken up?