This. I'm in the same position as OP (just started a history PhD this September) and I know from friends in higher years that everybody is saving for their "fourth year". While many expect to be able to submit by the end of third year (give a few months at most), there's still the viva and revisions to do which add time.

While that's not full time, you also need to take into consideration that academic jobs typically start in September (at least in the departments I have worked in) so if you're not done and dusted by September 2019, you're likely to not get an academic position (if at all, job market and all that) until September 2020 and you still need to eat for that year.

(I know one girl who's adamant to finish by September of her third year - that's September 2017 for her. She's currently FREAKING OUT about having to get the writing done so she can submit by late sprint/early summer next year. I don't see it working out like that.)

If it's money you're worried about, consider TA'ing. I have to TA for my bursary (not quite lucky enough to be AHC/ESRC funded myself) but any extra I do and any TA'ing I do in my fourth year will be paid at a decent(ish) rate. However, that may not be possible in all departments and pay might vary too obviously! I find TA'ing for most courses I'm on to be quite easy but again, that might vary from department to department so do your research before your commit.