Hi Amitchetu,
Based on my understanding, you want to create a subscription to send the report with email attachment, and you want to specify the attachment with dynamic name, right?
In Reporting Services 2014, by default, the name of attachment file sent with email subscription is the report name. It's not supported to format the attachment file name currently. In your scenario, if you want to specify the email attachment with dynamic name, you can create a file share subscription to generate a file name dynamically with report name and timestamp. Then schedule any SSIS job or windows job to do the E-Mail Delivery for the shared file.
If you have any question, please feel free to ask.
Best regards,
Qiu