I always front-load my campaigns. I try to keep them confined to one large locale (one planet usually), with a large scale storyline that has large events and a decent sized cast that the players can react to. This can take a good long time, but is often well worth the effort. Because then I can do a solid, memorable campaign with only an hour or so prep work for each session. Often, I just have several pages of stats for 'things I might need', and a list of generic names (with a character trait each) that I can use for very minor characters as needed.
See, this is much more sensible than what I did, which was give me players a campaign that has sent them tearing across the galaxy!
I don't think that matters. Setting and actions don't lessen or increase prep time. I've done sessions where the PC's stick around a while and ones they visit different places and both have the same amount of prep. You might have less research to do because you already know your setting.