One of the configuration for parachains is validationUpgradeFrequency which is currently 14400 blocks (1 day). This means parachains there needs to be at least a day duration between two runtime upgrades for a parachains.
This is a very big limitations for parachain teams. It means if an upgrade is buggy (e.g. missed a migration, breaks transaction version unintentionally, some new feature doesn't work), the fix cannot be applied during this 1 day cooldown period.
While there are many technical reason on why this number cannot be too low, 24 hours was picked as a conservative number when launching the parachain feature. We should be able to reduce this number to a lower value to reduce the cooldown between parachains upgrades.
After a chat with Rob, he suggested we could reduce the cooldown time to 6 hours.