I pretty much don't even try to write if anyone is going to be around, or if there are things I need to do (like work :) ). My "straight writing" time is usually when people are asleep or out, when I don't have other things I have to do, and when I'd otherwise consider the time "free time". I write in what might otherwise be "TV time".
Having said that, even though I don't do "straight writing"/"real" writing when there are likely to be distractions, I'll do "little extras" or "writing related" things when having one "chunk" of uninterrupted time isn't important. Tweaking Hubs, organizing writing, answering comments, etc. I just always have a few screens opened and have a few different things going, even when I'm working. Doing the smaller, non-straight-writing stuff whenever I can means I don't have to spend "straight-writing" time doing the smaller stuff.
That way, it's usually reasonably easy for me to find an hour (or even a few hours) just to write and do nothing else.