Try to see if you can persuade your employer into allowing you to have a day off, once per week, even if it means working extra hours on the other days. They will not always loose you for one day per week, as there will be school holidays.
I'm very cynical about distance learning. It's probably true you'd struggle if you went into an HNC class next week but you won't be doing that. The start date will be in September so you have the rest of spring and the whole of summer to prepare yourself for starting the course. You can spend time asking here and reading about what your need to know on the Internet. I'll even give you some of my old notes for the HNC/HND I completed 8 years ago if yoou like. Not much will have changed since the, you'll still have to learn algebra, calculus, Ohm's law, Kirchhoff's circuit laws, LRC circuits, Laplace transforms etc.
Back in 2006, the course was a bit Micky Mouse but going from what the apprentice where I work said, Bedford college has improved a lot in recent years. They've invested a lot in engineering and now have a dedicated engineering block and have made the course much more rigorous than before.