Okay, I've ended up pondering this 'timeline' thing a little more where the Bespin scenes are involved, lol....
Although this window shot (seen immediately after the Falcon's intitial approach / landing at Bespin City) was given an SE 'orange sunset' makeover to tie it in better with the previous shots, rather than the suddenly 'blue daylight' originally seen at this point in the GOUT, I've realised the other things that also contributed to why I always thought this was a 'sunset' arrival, rather than a 'sunrise' one....
When the above scene ends with C3PO getting shot unbeknown to the rest of the group, we then immediately cut to a NIGHT-time setting for the next scene that shows Luke deciding to fly off from Yoda and Dagobah. But when we eventually cut from this 'night-time' scene back to Bespin again, we now see scenes of 'bright daylight'. It's this 'flow of light' in the order of the scenes onscreen that has reinforced this impression for me - First 'Sunset', then secondly 'night-time', then thirdly 'bright daylight'. That's what gives me the impression that the 'bright daylight' scenes are meant to be during the next day, after they arrived. However, I realise that there is no reason whatsoever why it can't be 'daylight' in the Bespin system system and 'night-time' in the Dagobah system at the same time during these unfolding events onscreen. Equally, there's no reason why they have to be either, considering we don't know how far apart they are, or how often either has 'sunsets' or 'sunrises'....
The other things (apart from the sky colouration) that always gave me the 'sunset' arrival viewpoint, were that when we DO revert to 'bright daylight' scenes after the 'night-time' scene on Dagobah, is the fact that Leia is shown in a totally different outfit by this time, with a differently-styled hairdo also. Again, no reason this 'change of image' couldn't have happened from earlier in the same day, had they arrived at 'sunRISE'....but to me it just reinforced visually that a longer 'passing of time' had occurred, and could be showing the NEXT day....
Finally, back to the question of why Lando would have to wait to betray the group to Vader and his troops until the next day, considering he tells them that they'd arrived just before they did....well why didn't he just lead them to Vader IMMEDIATELY in that case, rather than spend ANY time whatsover accomodating them before doing so?..... Possibly because Vader wished it so for various reasons at that point, and Luke's flight towards Bespin from Dagobah takes an undisclosed length of time onscreen after all....
Either way I'm happy, but I just hope Ady doesn't end up 'yellowing' up his amazing skies.... I always loved those 'orange' hues....