Thanks for all the feedback, everyone!!
It depends entirely on whether you see Land selection as character background, or as a mechanical choice.
Yes, I definitely think this is key. This would be leaning more towards the latter. Or you could say it's changing the fluff. The suggested default about connection to the land where you first learned to be a druid would be changed to something like a connection to the land you are in as you attune to it.
I will say that I've got a homebrewed "Circle of the Seasons," where the druid's abilities change depending on what season it is.
Can I ask what area of the class mechanics you have changing each season (e.g., spells, animal forms, etc.)?
As per OP, its a little over-powered.
In play circle of land is already very versatile, maybe more then realized on first inspection.
With some of the suggestions above, it should be fine.
The versatility is my primary power balance concern. I wouldn’t say the spells are uber-optimized or min/maxed for each land type, but
spider climb probably has more utility in the mountains or the Underdark than, say, the coast or underwater. And vice versa for
water breathing. Still, it’s not quite the open book versatility of a wizard’s daily spell preparation.
I like all the geomancer ideas!

Yeah, I’m thinking leaving it optional is too mechanically generous. Additionally, the fluff would be that the druid connects to/calls on the land they are
in, so mandating the change, whether fast or slow, seems to fit with that fluff pretty well.
Perhaps changing spells in a single day is too generous as well. The staggered or downtime methods may keep it more off the wizard’s toes.