Honestly, if you put some torque on the twist top tins, they seem to hold moisture pretty well (in fact, I've had them reseal with pressure change--so I needed to break the seal again). If you don't torque them down, they will continue to dry pretty noticeably. I have several tins that have been sitting in an unsealed for two years and the tobacco is still perfectly malleable--not turns-to-dust-when-you touch-it-dry.
Some random context:
--I tend to like my tobacco dry. Some blends, I find, lose flavor if they dry past a certain point--and some just become impossible to handle because it crumbles so easily--, but some I can leave sitting out as long as I want and still find it perfectly smokable (e.g., I once bought a tin of Old Gowrie that had gotten dented and lost its seal--by the time I got it it was basically at ambient RH. It was perfect). So for my preferences, even a month in one of those rectangular tins (that do not, btw, seal) is fine; I have a tin of Capstan that has been sitting around for over a month now, and it is fine for my taste.
--I like sharing an experience with smokers of the past. I can't imagine Carolina farmboys or sailors from (say) 1820 freaking out about how to maintain the perfect moisture of their tobacco. I suspect that most of what they smoked, they smoked at ambient humidity.
--I have found that bail jars don't actually seal for long-term storage. I opened one that had been sitting undisturbed for a couple of years, and it had definitely continued to dry out. Ball jars are probably better but
--I'm lazy.