Hi hitenrastogi!
>I want that variable to be preferably in something like alfresco-global.properties
Noone limits you, read whatever property you want from whatever configuration you want. You can use spring bean, java delegate or whatever JUEL-available configuration reader you want. TimerCatchingEvent simply runs JUEL expression to get timer definition. One of my processes reads timer duration from LDAP.
I don't think such property can affect timer jobs in activiti database, though. That is, once timer is set, it needs to be fired before it can change configuration (reread properties, reevaluate expression) .