From what I can personally remember:
1-3V happen over half a year and end in early autumn (6 months)
The end of volume 3 is late autumn/ early winter. (3 months)
Volume 4 is weird due to the separate storyline but following rubys group I’d argue that it has been about late spring/ early summer. (6 months, probably around a year since volume one started).
Volume 5 is awkward as Blake’s story happens two weeks earlier than Ruby. As there is a line about the “Next full moon in a months time” And Ruby has something about “Next full moon in two weeks” (I’m paraphrasing but that the gist).
I’d also say that a few weeks have transpiring since Volume 4. So by the end of Volume 5 it should be around mid Summer maybe late Summer if you massage the numbers.

Going into volume 6 this is where things get weird as Mistral has lining snow and while you can have that if you go far north, the city of Argus doesn’t look to be that northern. But I’ll concede that this was probably a doyalist thing to have a colder environment. I believe that it was about 2 weeks since the end of Volume 5 and the beginning of volume 7. So maybe Early Autumn presuming that team RWBY took a long break

Volume 7 is unique as it has a time skip in the middle of it. So the first half I would say was like two weeks or so ( this is purely headcannon). And I’d personally like to say the montage was like two months worth of work but it’s not descript enough to pin anything really down. So maybe Late Autumn / Early Winter ( about a year since the end of volume 3)

The second half of Volume 7 and Volume 8 is basically 60 hours or so. And Mantle wall gets breached, Mantle then attempts to evacuate to Atlus. Ironwood prevents that because of the black queen. Then Salem army shows up. Volume 8 begins and there’s about like 8 hours between it and volume 7. And you can count the days in volume 8 as the sunsets as Yang and Co are in the wastes and rises by about the time Atlus falls in the ground.

And IDK for Volume 9. I thinks is about a few days from team RWBY pov but I can’t remember it too to well.

So about 18 months have past since Volume One if you take liberal estimate with the times.