Is there any way to limit when hotspot users are allowed to log in? Would this only work through a radius server? For example, is it possible to limit users X, Y, and Z to only be allowed to log in during certain hours of the day?
A RADIUS server would always be a good solution. But you can also make his work by writing two scripts: one that disables the local the users and removes all active sessions for the account, and another one that enables the account again. Then schedule them at the appropriate times.
what ROS version are you using and which user-manager package installed ?
if you use ROS v4.x than use user-man-test package and you will be able to the limit as wishes