There is no grouping in user setup.
However, there is a way to set up two "groups".
Group 1
Set blank on the Allow Posting From and Allow Posting To on most users.
They will take the value from General Ledger Setup - Allow Posting From and Allow Posting To.
Group 2
Set the Allow Posting From and Allow Posting To on the User Setup.
This means you only need to worry about users who have special need for posting on specific date on the User Setup.