I have to develop a workflow,where admin user has an ability to select date to complete that workflow.
E.g. as soon as workflow notification comes to admin user, he can review the content and select a date so that page can be published.
Is there any OOB functionality available?
AbsoluteTimeoutHandler
is what you're looking for. This can be used for scheduling the content publishing based on user entered date in the workflow participant step. – Abhishek