Acknowledge any inquiry within 5-10 minutes unless on a lunch break. Otherwise it means you are afk.
(edit) To elaborate - there are two issues involved with this. First is that you are unlikely to ever work on a fully self-contained task that doesn't require collaboration with other people. As such having shared work hours is required. Second issue is that of trust. In common tongue "working from home" means "sleeping in, sitting on a couch, going for two hour lunch breaks, etc". It's a way to slack while pretending to be working. I'm working from home, wink, wink, quote-unquote. In a perfect world you would be judged on deliverables and perfectly met deadlines. In real world, you will frequently need to prove that you've been working and that 1 page of code has indeed been a result of a week of research and numerous rewrites.