You need to somehow narrow down your options.

Fair enough. I always want to do everything at the same time. No calendar, AI sounds interesting... but give me a few days and I'll give it some serious thought.

... how much time and energy you've got to spend on the problem.

The upper limit, which I'll fully invest without hesitation, is:
1.5 semesters (4 month, 3 evenings(1800-0100) per week plus one full day(1200-0300) per week)
1 summer (3 months of which half can be spent full time(1400-0500) on the project including weekends plus the evenings(1900-0100) of one month). It's a single person project, I tend to work slow but exact (over-engineering) and I need to thoroughly document the whole thing.

Assuming 4 weeks per month we get 1.5*4^2*(3*7+15)+6*7*15+4*7*6=1662 man-hours minus bath breaks minus time to prepare(not eat) food.

Sorry for the awkward way to express this but I don't know about a standardized way to calculate man hours (though I'm sure there is one somewhere).