Some people will very decidedly focus their MMO play time around accomplishing certain goals. It doesn’t matter if it takes five minutes or five hours, they are going to play their games until they finish their objectives. Other people log into MMOs for a very specific amount of time. They’ve got kids or chores or other things that require taking care of after a certain point, and that means that it’s time to take care of what you can during a fixed duration and then move on afterwards.
Obviously, there are no laws requiring you to just do one or the other; you can alternate between them on different nights. But as a general rule, I think most players pick one or the other. So which do you prefer? Do you structure your MMO play sessions around playtime or overall goals? Which feels more satisfying and lends itself more naturally to your play preferences?