I read the OP as these specific work colleagues had discussed the issue with her and were disturbed by late night emails. It might not be rude, objectively, to send the emails whenever, but it just doesn't seem wise to me to do something you know irritates your colleague, when it's not something you have to do. Of course there is a fine line there, which we discuss here all the time--is it rude to play soft music/eat fragrant food/make work-related phone calls at your desk/be more successful than your colleague, if it bothers your colleague? To me, since there are so many other options besides sending an email right then in the middle of the night, I think it's worth waiting, and not irritating the colleague.
This is kind of the situation. It's more that I know that they read them because they respond straight away.
There were a few weekends recently where myself and another manager agreed between us not to send any emails to our (mutual) boss over the weekend because we were worried about her and didn't want to give her more work! (That might sound patronising to some, but the type of things we would send were things that really *could* wait, and we knew she'd been burning the candle at both ends and desperately needed some family time). We both did the work we planned on doing but just saved our emails up to send on Monday. So there's been no complaints but both her and the other manager have young children and both tend to work long hours from home (as do I), so that switching off time is important. Of course they are adults and will make their own choices and switch off their phones as needed, but at the same time I don't want to add to the problem. Like I said, I'm exactly the same in that I too will reply when I get the emails! Which is why I have alerts switched off so although I check them constantly, I don't get actually interrupted by them. I only see them when I'm actually sitting around playing with my phone or sending emails etc.
Anyway thank you all for your comments it's an interesting topic. I've been booked for induction early this coming week, so we decided it made sense for me to actually stop working as of Friday - which included completely disconnecting my iphone from my work email because we all know I'll keep checking them otherwise!
So it's a moot point now as there's a gap between work and having bubs after all. But of course the topic is still relevant in general. I guess every situation is different so I'll keep it case by case.