for my mech eng degree, we pretty much did a maths degree in our first year, in addition to everything else – nothing in the 2, 3 and 4 year would have been possible or made any sense without it.
Depending on where you go, it’s not something I would consider you could do on day release. Admittedly I finished my degree about 11 years ago, but even then we were doing a 28 hour tutored week, and there was lab time and study time on top of that, I reckon I was putting in a 40+ hour week consistently over the 4 years. Sure, you could get away with less, but depends what you ultimately want to achieve.
Coursework was generally epic, again involving lots of lab time, leaving things, checking them periodically etc, and never quite walking away from it. Lots of presentations and question / answer sessions too. In terms of incorporating it into the current role, that may be course specific (I know mine we couldn’t), although a year in industry was possible, that would have taken it to a 5 year course.
If I’m honest, it’s pretty much a full-time “degree”. You may be able to do other mech eng courses that have lesser accreditation on a day release basis, but I reckon to do well at that and work full time you’d be kissing goodbye to pretty much any social life.