Roll20's saving grace in this situation is you can offload the Winter Phase and solos to the campaign forums. Even with that, from previously GMing Pendragon, I can't see knocking out a year/adventure in one session. My Swords & Wizardry group recently fit in 43 sessions over the span of a year (with holiday breaks and playing other games). So, 86 in-game years means 172 sessions - taking exactly 4 real life years to get through.