I have an implementation of a single ProxySG which is serving more users all around the World.
What can I do to limit the browse time of this different users, let's say from 13.05 to 19.00 with the different time zones ?
Using any time converter website tool, perform a conversion from your time to UTC time to see the difference (ex: http://www.timeanddate.com/worldclock/converter.html).
For example 13:05 EST would be 18:05 UTC time.
In the Visual Policy Manager, when creating a time object you can use either Local Time or UTC Time.
To see what the ProxySG has as your local/UTC time, click on the Configuration page -> Clock. Pick whichever time works for you.
ProxySG can update automatically its own Clock Time, using Time Zone or a NTP server. However Time Object Policies will not be updated automatically (ex. in case Daylight saving time is applied to the time zone in use).
Perform a time conversion so that you configure on your ProxySG time according to your zone, accounting for the conversion to all other time zones you need to configure. (Ex: Configuring a time object for 13:05 UTC time, so it would be in effect at 18:05 EST).
To make sure the time objects are not applied to all your user base, you have to define a source object in the same rule. If you're using AD, hopefully you have different Site OU's you could call into play.