Bunnies cope well with cold, heat is much worse. Unless the temp diff is more than 10 degrees C (sth like 17 F I think), the bunny can adjust. Draft is not good though.
Perhaps you could get him a vet bed to sleep on at night (it’s like Sherpa fleece with anti-slip under) or perhaps he could have a night light like children have?
I don’t know if they do get afraid of the dark, but perhaps some buns do and others don’t, like it is with dogs.

24-23C is more than warm enough for your bun. Around 15-21C is ideal, but not always realistic. I keep my place at about 23C in the summer and between 18 & 20C in the winter.

As bam mentioned, as long as there’s not a quick and drastic change in temperature, your guy will likely be fine in what’s comfortable for you. It doesn’t hurt to offer him something soft/warm nearby. Since he’s free run (?), he’s able to leave the window sill if it becomes to cold for him.

As for the night light, I don’t know if they’re afraid of the dark, but they do sleep differently than people. He may just enjoy watching the cars pass. My girl is free run, but when we visit my parents she’s in a a small enclosure which she escapes every morning so she can sit directly in front of the window and stare outside.

He’s inside-unless you are wearing a jacket it’s warm enough And he can leave that spot but obviously likes it Should be just fine!

I believe too that if he has other warmer options but still chooses to be there, then that is where he’s happiest!
Mine too chooses to lay right up against the cold windows on cold tiles with the nice ‘warm’ carpet just a few inches away… (and I haven’t seen her shiver yet. lol).
Also if the rabbits are laid out at full stretch then they’re not cold (or they would be hunched up in a loaf, like cats or dogs (and us humans) do to retain heat).
Atleast that is what my non-veterinary-training logical mind says. :o))