I worry that a DM would run this by just reading the scenario and asking for a group check, and then giving the result of the check, which would be terrible (IMO). I can see freeform, as you intend, being good when done well, though.
I assume that you mean the DM calls for the check, the players succeed or not, and the DM says "OK, you've made it past the challenge," and that's it, instead of at least narrating the events within.
There's a large part of me that worries asking for a single group Survival check isn't enough. However, there are other rolls involved, so I'm not sure how many Survival checks would make the whole thing feel right. Part of me wants to call for one check each hour--which is still only one check in the case of the Acid Fields and Corrupted Grove.
(I will say it's odd that a place that only requires an hour to traverse would add an additional 1d4+1 days to travel around.) Bolding for emphasis, and for requesting an explanation.
Lemme try out the Acid Fields here and see how it looks. I'll assume I'm running for my current party of five PCs, who are about 6th level (so, half the party, meaning 3 PCs have to succeed because I'm going to round up). So, three succeeded (I rolled!), so they pass. No particular hazards.
I describe them as seeing acid geysers go off, occasionally almost stepping in sizzling puddles, and seeing the corroded bones of creatures that weren't as lucky. Let them explore if they feel like it. Hmm... I can see the rogue, who's day job is herbalist, wanting to see if there are any particularly hardy acid-plants around for her to harvest. I'm going to assume that this would be covered using the "gathering supplies" rules, which I think you said are going to exist. Doing this would increase the time spent here, which would increase the chances of getting caught in the acidic spray.
Halfway through, I have them roll a Dex save--I assume it's still 15--or get caught in an acid geyser. Do I have them roll twice, once at the half-hour mark and once at the hour mark, even though after the hour they are leaving the field (assuming they didn't stay to look for stuff or fight a monster)?
Also, now I'm slightly confused and/or annoyed. The fact that they are walking at a slow pace should maybe give them advantage on their save against the geyser, but letting them avoid it completely? That kind of takes away from the fun of having an acid field in the first place!
And it kind of assumes that they're traveling from A to B for a distinct purpose and have a time crunch, where walking at normal speed would be preferable. If they're just traveling, as many parties are wont to do, then they don't lose anything by traveling slowly and they gain auto-success.