Just me but I have found that to be the opposite of what I need. It is generally warmest in the early part of the night and gets colder as the night goes on. I found that hot water bottles give heat early when not needed as badly and then cool down to no longer be helpful in the wee hours when the most warmth is needed.

BTW, one of the things I find most helpful is to be careful to not be warm enough to sweat or else you get colder later. So I adjust zippers and drawstrings to be slightly cool and close up more as the temperature drops. In places where the day night temperature differential is great, that might mean starting out on top of the bag and progressively draping it over me, climbing in, zipping up, and pulling the hood drawstring tight (breathing only through the face hole and never into the bag)

Also as has been mentioned having really dry clothes for in camp and especially completely dry socks to sleep in is a huge help. For cold weather I have a dedicated pair of thick socks worn only in camp and for sleeping.