This could lead to unbalance among the classes
This answer assumes that the party will still have a similar number of encounters per 24 hour period.
As CTWind's answer pointed out, longer days will effectively nerf any spell that has a duration of 1 hour or more and doesn't replenish on a short rest. This also nerfs almost all of the caster classes, as nearly all of them only replenish spell slots on a long rest.
Magic based classes will be weaker
A wizard, for example, is a powerful class because they are incredibly versatile and can cast so many spells between rests. But, they can't get those spell slots back without a long rest, meaning your wizards will have to be very reserved about which spells they cast and when. Classes with fewer spell slots, like the sorcerer or cleric, will get hit even harder, because they have far fewer spell slots to begin with.
Mixed classes will also suffer
"Mixed" classes that do both combat and magic, will still be impacted, but less so than the pure casters. The ranger, for example, often relies on a mix of magic and combat to be effective, though it relies far less on magic than the pure caster classes do.
Non-magic classes will probably be fine
Non-magical classes like the fighter and rogue I think will be impacted the least - especially the rogue, which often relies heavily on being able to sneak and use bonus actions, neither of which has any constraints on how often they can be used.
The non-magic classes will be stronger compared to the other classes
This will (generally) result in the non-magical classes becoming stronger relative to other classes, with that discrepancy growing the more reliant on magic the other class is.
There are a few exceptions though.
Low-level barbarians will probably suffer more than, say, a fighter or a rogue, since they only have a limited amount of rage between long rests. By stretching out the time between those long rests, the barbarian becomes much more vulnerable, at least until higher levels.
Paladins will also be impacted, though I'm not sure to what extent. I've never played one, but I know that Paladins are a "nova" class, meaning that they can do a genuinely stupid amount of damage all at once, but then they can't do that again until they get a long rest in. Extending the day also prolongs the downtime between paladin damage bursts, which could significantly reduce their damage output. That said, Paladins are also just really good at soaking damage and dying very very slowly, so that might not be as big an issue as I think.
Then there's the warlock. Unlike other magic-based classes, the warlock restores its spell slots after a short rest. This means that while the wizard, sorcerer, druid, and so on are carefully conserving their resources, the warlock is free to cast its spells with no regard to the longer daytime hours! As long as it can get in an hour of downtime here and there, those spells can keep on flowing! This is effectively a buff to the class, rather than the nerf that other caster classes get from this!
If you're going to do this, treat it as a playtest
I don't know to what extent this will actually impact your game. You might try this out and find that with your pace, the game isn't really impacted at all. On the other hand, your pace might lead to some really unusual balance issues as described above. I haven't done anything like this, so I don't actually know how noticeable the impact will be. So, if you decide to play this way, I suggest treating it like a playtest, and be ready to tweak the game to try to keep things balanced. Just make sure your players are alright with that beforehand!
On the other hand...
If players and DM are both fine with it, exploiting a broken mechanic can actually be a lot of fun!