IIRC, there’s a WEG sourcebook that established Luke spent six months on Dagobah. Wish I could make a proper citation, but the Googles do nothing.
Sadly, the relevant pages (pp. 96-100) from The Movie Trilogy Sourcebook found on https://www.starwarstimeline.net/Westendgames.htm seem to be working hard to purposely avoid any mentions of actual measurements of time. The author saw the problem of space being really really really big though, and says that the Executor gets to Bespin first “easily beating the Falcon’s aged backup hyperdrive”, thus explaining how they were able to get to Bespin at all.