From my experience booking and re-booking our cruise tour from 2020, to this year (2021 was a wait and see year for us) it was about 12-14 months out when they started to appear on the website. Now some of that may have been the line holding back to see what was going to reopen after the whole mess of covid.
What I did was book the cruise, then when the land portion opened up rebooked the cruise tour. That way we knew we'd have the stateroom we wanted instead of waiting it out for the land portions to open up. It actually worked out pretty well seeing that before they disappeared from the website, we had paid about $2000 less than they were going for at the time.