Hey Solluk!
While yes, we usually run month-long missions, that's usually something up to the CO and XO of the ship. I'd suggest you talk to them about things.
For example, The Discovery recently ran down a rather long mission that extended for over a month. From my own personal experience, missions are usually terminated on the month because activity drops too low to keep it going. Provided activity is OK, I'd say talk to your Ship's Rep and the chain of command to see if there's a particular reason your team does monthers!
Hope that directs you to the right people!