You cannot reschedule a deployment after it starts:
Select the check box for an update.
Because all devices do not need to have the update deployed at the same time, you can set individual deployment schedules for the devices.
Click Action > Reschedule Deployment to open the Redeployment Schedule dialog box.
Either click OK to accept the default schedule of Now, or select Date Specific in the Schedule Type field, specify the new date, then click OK.
Select the check box for an update.
Click Action > Reschedule Deployment.
In the Status by Device page, select the check box for an update, then click Reschedule Deployment.
On the Status by Device page, select one or more devices that are listed in the Device column.
Click Reschedule Devices to open the Redeployment Schedule dialog box.
Either click OK to accept the default schedule of Now, or select Date Specific in the Schedule Type field and specify the new date, then click OK.