no - doesn't look like that piece of data is exposed on the text construction for the notification list.

Unity 7.0 did include optons for customizing subject lines which I thought might give you a backdoor way to do this but the original sending time is not a parameter you can put in:

http://www.cisco.com/en/US/docs/voice_ip_comm/unity/7x/release/notes/702curelnotes.html#wp69476

I think the assumption there was the time on the notification itself would be sufficient, however for inbox notifications you can get a list of messages repeated over a period of time - original sending time would be handy to have in that list. I'll pass it along to the Unity dev team.