how can I add timestamp to subject line of unbounce notification email?
Even on the Pro and up Unbounce accounts which allow more customization of the email notification, I don’t believe inserting a dynamic variable like a date is possible.
You have a couple of options here:
Write your own webhook/script that creates and sends the email. A bit more information about this options is available here.
Try doing it through a service like Zapier that works wonderfully with Unbounce