Most contracts I see these days define it as work that could be reasonably seen as in their line of business, or using company equipment or resources (e.g. internet). I can't remember the last time I saw one that made a distinction based on clock time that wasn't also for a 1099 contractor. These days it seems it either goes "All your thoughts are belong to us" or "using our stuff in a market we sell to".

A reasonable definition of "on their time" for a salaried employee would be things they asked you to do for them. (Presumably they did not hire Arandur to write HN comments.)

Another IMO reasonable definitions:

- you used company equipment for that == it's ours

- you billed us for the time which you spent on doing that == it's ours