any temp difference bigger than 10c for any long amount of time will cause issues and could even cause death due to overheating or becoming too cold too quickly.
I really wouldn't say any difference whether they are 6 months old or 6 years old, the temp difference will cause problems. they can not take their winter coat off no matter the age. yes younger ones are able to adapt more, but its still not recommended.
the moment you bring them in to a heated house they'll start to moult as its too warm for them. no rabbit its going to keep its winter coat on when its in a 24c house or so. think about how they feel, they can not take their coat off right away, so they're going to be in 20c temps when they're used to 10c or less. it hasn't reached over 12 where I am and usually is as cold as 3c. its rather cold now and while some years its much warmer in november making it easier, this is one of the cold novembers.
to bring them in so they keep their winter coat you're going to have to put them in an unheated room with the window open so the room is the same temperature outside. actually if you bring them in at all you'll need to bring them in to an unheated room that its the same temperature outside. and then once she is recovered, she can go back out with no complications with any temperature differences.
if that isn't possible then I would say wait until next year in the spring/summer to get them spayed so its not as big of a temp difference.
I'm not looking to play down your experience Angie, but you were incredibly lucky IMHO for your bunnies not to suffer health complications and/or lose their winter coat from coming in for such a length of time. research does agree, as does the RWAF whether you take their advice with a pinch of salt, that bringing rabbits in and then out for long periods of time can have health complications. either your utility room was very cold, or it was a warmer november so it wasn't too much of a difference, or you were incredibly lucky.
when I brought my outdoor in all he could really do was lay there breathing heavily as he was too warm, that was in october 2015.
its really not a good idea to bring them in with such temperature changes now. theres too much of a risk and too much at stake. health complications such as blockages due to the amount of fur their ingesting or just ending up overheating could pose serious issues and its not something I would personally play with.