alt Hacker NewsReply 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!
Your kids getting picked up shouldn't depend on you seeing an instant message, that should probably be agreed upon the previous day. Sure, emergencies happen, in which case you can't really be held responsible. But if that happens more often than not, that's bad parenting.
Or maybe your agreement with your spouse is to communicate over instant message about managing these daily tasks, in which case it's ok, but you better crank that notification sound all the way to 11 LOL