Mmmhh.... I am not sure it's necessary, but I see nowhere "Timer - Show timer for All players" or something. Maybe would it fix a little more your trigger.
Also you should do : (sry I don't know how to use the [trigger] tags)
Notice that you have to set the variable "timer", that I used for that Start Action, Start "timer". You can use another variable if you want to.
Your trigger can't simply work, because you want to start the timer "Expiring timer". It's simply not possible, because Expiring Timer is an event answer, and so in your event you should have been put "timer expires" or something, then this would have been possible.
Anyway, try with my method, I think It'll work :).