Noah Tucker straight TOR as well as Darkening of Mirkwood suggest one adventure phase per year. So you go do adventure phase stuff for as long as you want (typically keeping an eye on fatigue and shadow), then you do a fellowship phase, and then you play next year. 

There’s some creative/logistical space there where you can do additional fellowship phases kind of…whenever. And to be honest I’m not sure what the rules say about how long a fellowship phase “has” to be. Like, if you were really hard-nosed about gaming that, I have no idea what the balance is. Like…go do a small thing and then take a break! Burn off that shadow. Now go do a thing and take a break! And burn off that shadow. And so on. 

it’s a gap in the game that nobody’s tried exploiting yet, because I’ve framed it as “do what you want all summer, then go winter somewhere and take your fellowship actions.” It’s very similar to the pace of The Great Pendragon Campaign, which they’ve been a good ways into.