PEx 've already had a useful command: pex user <user> group add <group> [world] [lifetime]

But incase we run this command again for a user with same group, the lifetime will be overridden with new lifetime. It would be great if there's a command like pex user <user> addtime <group> <lifetime> [world]
to give more time for that user to be in a group

No new features will be getting added to PEX 1.x, but @zml2008 may consider doing something like this for PEX 2.x since it's still in development.

Unfortunately PermissionsEx is currently unmaintained and no further updates are planned. Because of this, all pull requests are being closed. If you are looking for an actively maintained permissions plugin, take a look at LuckPerms. It is compatible with major server platforms and can import data from PEX.