They pretty clearly spell out that Jabba has Han and that they will be meeting at a distant point in the future at the rendezvous but to have planned it for a full year away seems a bit unplausable. All I can think and read into it myself is that it took a lot longer to get everything in place that they planned
For Lando to create a character, gain trust in Jabba’s crew and become “one of the boys” had to take same time. We’re talking about the galaxy’s greatest gansta’ leading the galaxy’s greatest gang. You don’t just walk into that place, buy the room a drink and get accepted.
Luke has clearly advanced in skills. There’s certainly some time tied up there.
The entire Rebellion has evaded the Empire, regrouped and found a temporary place to hide while also fining out about the new Death Star, examining the layout and finding a way to destroy it.
A year seems easily plausible to me.