Shared mailboxes and calendar on online mode instead of cached

Hi,

I have users that share a calendar but when one of them adds something to it on their own pc, it does not show up on the others until a very long period of time. Now my aim was to have their own personal mailbox cached and all shared mailboxes and calendars on online mode. That way I think the calendar would synch significantly faster to all users viewing/using it. 

Hope someone can help or guide me on how to do this. 

thanks