Im brushing up on my 6502 over my lunchbreaks, maybe working up to a c64 game or demo, but i dont do that during any other part of day. Given I work in games , i recognise theyd have first dibs on anything valuable. in reality I have a long way to go before that would likely happen .
If an employee is working on a non-approved side project while they should be doing more boring work thats not cool. I would say if you have downtime at work check with your employer first and find out how they would feel about you making better use of it. Nowt wrong with asking ?