Didn't see the point when you first posted with an example in part of the event declaration, didn't make sense and wasn't something that couldn't already be done.
However after you gave a better example i like the idea, if would prove very useful for mirc to trigger any appropriate 'when' declarations at the point that the var/identifier/etc is changed, and as you said would make some things that usually require timers much easier.
a timer that calls an alias every xx minutes/etc then performs some tasks or messages could be made much simpler with something like when:$sometimedateidentifier // %varwithdelay:commands
of corse thats a simple use, but this type of thing would also avoid the need to start/stop/restart such timers.
a command (like /timers) to list these type of binds would be useful also