>>11093990depends on how motivated you are towards the material. if you're really interested you can easily go for full days, much like you could play a hard puzzle game non-stop if it's good.
if the material is dull, then you're probably not learning much by doing it, and you risk killing motivation towards even other topics by association. if you have dull math to do, add other topics to keep interest up.
the rest is standard work-life balance; the most important limits are stress and isolation.
if you're doing math professionally or as a student, the stress is from outside pressure, not math itself, so doing more math shouldn't be more stressing - it could even help you keep up with work better.
if it's a hobby, math is only stressful insofar as it stops you from doing more important things.
isolation can be tough, but the gold standard is to do math in pairs or groups. should be doable for students and professionals, much tougher for hobbyists.
daily lunch break company and the odd weekly meetup is probably enough to get by if it's the same people every time.