Mania = a few weeks and then I usually get in trouble for various things like yelling off bridges, climbing things, etc.
Depression = months.

The depression seems harder to treat.
I have a hard time recognizing mania. People tell me things they notice but I don't believe them (like I am talking too fast or not sleeping or spending too much money, etc).
Since I miss the signs, I usually get totally off the deep end until I am "stopped."
With mania, they throw me in inpatient, give me some high dosages of meds and I am out in a week or so.
Depression just lingers.. it sucks... even if they throw me in inpatient, it still takes months to get better.