Quote:
man# man useradd
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USERADD(8) USERADD(8)
NAME
useradd - Create a new user or update default new user
information
SYNOPSIS
useradd [-c comment] [-d home_dir]
[-e expire_date] [-f inactive_time]
[-g initial_group] [-G group[,...]]
[-m [-k skeleton_dir]] [-p passwd]
[-s shell] [-u uid [ -o]] login
useradd -D [-g default_group] [-b default_home]
[-f default_inactive] [-e default_expire_date]
[-s default_shell]
-e default_expire_date
The date on which the user account is disabled.
Changing the default values
When invoked with the -D option, useradd will either dis-
play the current default values, or update the default
values from the command line.
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Use
-D if you want to change the defaults. If you have not done this before, you may not want to do this just yet

As for expire day
-e that depends on your security policy and how much grief you want to give users. Perhaps others care to give guidelines on this? (30? 60? 90? days)