I've never jarred after opening, but I tend to smoke just one tin until it's finished, so usually about 20 days (for a 1.75 oz/50 g tin). There's some though that I rarely smoke and they've been open for over a year (like my tin of SPC Plum Pudding Special Reserve). I have some others open for a while though, like months, usually virginias will be open for half a year before I finally finish them.
I do usually put open tins in a gasketed food container though. It's not perfectly air tight like a vacuum sealed bag or vacuum sealed jar though. Not always though, depends.
They all do stay in a cabinet though. It depends on the blend. I've been smoking through Kopp YotD and that just sits in the cabinet, not one of the bins, and it's been open for almost 2 months now, but it's also almost finished.