@AMRITASINGH Calendar is a data object and cannot be a delegated rule.
If you want a better experience, you can easily create your own harness that will render the same section as used in the ruleform. create a DP that will load the calendar data and run the section 'Schedule' against this DP. You will then have to implement the save button using a run activity.
The other option is to circumstance the ruleform harness using the portalname as circumstance but you will still have the calendar opened in a different window and it will not use the Cosmos skin.