This might come in handy for those of you who work outside of hours like me.
From time to time I find myself thinking of a problem after hours and when I have that eureka moment I like to get the ticket solved & out of the queue, but at the same time I dont necessarily want the user to see that it was answered at 11pm
I use a combination of google apps for email, boomerang for gmail ( http://www.boomeranggmail.com/ ) to schedule the tickets and zendesk's mail API to set tags and status etc
So I reply to the ticket via email, schedule to send it and the relevant time and more on.
Some screenshots of what I created are in this link http://alanconroy.clarify-it.com/d/wrnxm6
There is also an outlook version of boomerang if you dont use gmail/google apps