I see this in the opposite direction at work. I'll send someone a chat message after their working hours and they'll actually reply apologizing that can't look now and will reply tomorrow. Or that they're just waking up and they'll look later today. Yeah, that's what I expect, I'm not your boss asking you to come in on a Saturday. Why on earth are you looking at your work chat outside of your work hours anyway??

Reply time to instant messages is extremely context sensitive. If I'm having a chat catching up with an old friend I haven't talked with much in a while, I might take several hours to a day or two to write the next message. If I take a day or two to reply to my spouse's inquiry of "what is the plan for dinner tonight?" or "you need to pick up the kids from school today, ok?" I'll have some problems!