There are a few places where Single displays the release date of a digital album:
On the digital album product page (if published with audio player)
On the "Your Download Expected" post-purchase email
On the delivery email for instant grat tracks
Using Single's Confidential Release feature, you can hide the release date from the above. This option also disables the "Your Download Expected" email entirely, so fans only receive an email from Single when the album is delivered on the release date.
Steps
Navigate to Music > Digital Delivery from the left side bar. You'll have the option to either create a new digital release or work with an existing one.
Find the Confidential Release switch in the Scheduling section and toggle it on.

