The employment lawyer I consulted a few years back stated all work done outside office hours is essentially implicit property of your employer in Canada/UK... unless explicitly stated in your employment contract that external unrelated projects are your own.

In most of the US, all work done outside of your employers business is implicitly your own... unless explicitly stated in your employment contract that they have rights to such works.

In general, most commercial businesses won't care unless their IP or resources were misappropriated for a personal project. Best of luck =3