As of 3/10/09, the ability to hold medication orders has been disabled. There are two options that can accomplish a hold:
Edit the active order, changing the start date and time to the hour you want the order resumed. (Change orders are sent to the pharmacy as an order to discontinue paired with a new order for the change.)
Discontinue the active order, and write a new order for the same medication, with the start date and time set to the hour you want the order resumed.