The tutorial on them says:
This is used to add the name of an entity your multi_manager will be targetting, as well as the time (in seconds) that entity will be targetted after the multi_manager has been activated. In the Key: field, type in crate1. In the Value: field, enter 1. Hit the OK button to log the entry into the keyvalues area. You have just set up the first event in your sequence! The func_breakable called crate1 will be activated (blown up) one second after the multi_manager itself has been activated. Now hit the add button again and enter crate2 and give it a value of 2.5. Hit OK to log the entry. Now crate2 will be blown up 2.5 seconds after the multi_manager has been activated. Add the entries for crate3 and crate4, giving them whatever time values you prefer.
I know how to use them but the thing is, what if I don't want to wait 1 second before they fire? What if I want to wait only half a second? Or what if I want them to fire instantly?