Yes, a customer can change their delivery date via a couple different ways with Ongoing.
1) PAUSE OPTION ON SUBSCRIBER PORTAL
With Ongoing Subscriptions, a subscriber can pause their subscription on the Subscriber Portal, if they wish to not receive a package for a little while.
They can reactivate it when they want to start it up again.
2) SKIP NEXT DELIVERY ON SUBSCRIBER PORTAL
With Ongoing Subscriptions, a subscriber can choose "Skip Next Delivery" on the Subscriber Portal if they want to skip the next shipment.
After it skips a delivery, it will continue creating subscription orders in the future.
3) MERCHANT CAN CHANGE NEXT BILLING DATE
Alternatively, a subscriber can always email the merchant to let them know they want the package delayed and the merchant can mail out the package for the time-frame specified by changing the next billing-date on behalf of the subscriber, which will then trigger the order to be created on that next billing date. This is helpful if the subscriber has a specific date in the future, the merchant has the control to make that happen.