Should I start working as a teacher at a different uni while I'm still finishing my PhD? I am currently doing a PhD in maths, in the UK. UK PhD scholarship are typically only 3 years, and mine can't be extended. I do need every day of these three years to finish my thesis. For a small fee, I can hand in my thesis up to 1 year after the money has run out.

I now received an offer from a german university for a half-time teaching position in theoretical computer science. The position would start 3 months before my PhD scholarship ends.

Should I accept this offer? A similar question has been asked before, but there are a few circumstances that make the decision harder:


The university where I could teach is in germany. It typically takes a day to go from one place to the other, and it isn't too cheap. (There might be some financial support from the german uni.) So I would be meeting my supervisor significantly less often, but possibly this is not so much a problem towards the end of the PhD?
I would have to switch fields. While there is enough overlap between the particular topics so that I can learn the teaching material without too much effort, I'm unsure how risky this is for my career. In the worst case, I will not be able to establish myself in computer science because I would "only" have a maths PhD, and could neither return to maths because I left the field for too long a time. But again I'm not sure, how realistic these apprehensions are.
First you have to ask your advisor.  You can't just leave with 3 months left on your scholarship.  Angering your advisor is a terrible idea in a field where it's likely that everyone knows everyone else.

Second, you're going to be extremely overwhelmed at how much work it is to teach a new course.  Even though you're only teaching half time it's going to have a huge impact on slowing your thesis progress down. It's possible that you might not even finish.

However, you do have to take into account your finances.  If this is the only job you think you might get it might be necessary to pursue it so that you have income.