Originally Posted by vem

You can level up every day for quite a while, unless you mostly do 80 stamina daily missions which give very low XP.

Only certain stages from the main story will give reasonable exp to stamina ratios. I've only encountered a handful of event stages that can give good exp, but you can't rely on those to level up, especially since you'll be focused more on trying to get the most points to use in the event store rather than leveling up your commander.