If you use this medium for regulatory disclosures that require time frames. When do you consider that time frame beginning...when the customer opens the email or when the disclosure notification is sent by the bank? I was wondering if this governed by E-sign and UETA ? Lastly how would a bank monitor these time frames?

Delivery means when you sent it, just as with snail mail. You can't control and realistically can't determine when a message was received. It was available for receipt (assuming no backbones were down, etc.) And just because a machine received a message, that wouldn't mean a user was there to read it.

The Fed's 2001 amendments/commentaries to Regs B, E, M, Z, and DD specifically indicate that delivery occurs when you send the message. For other laws & regs you'll have to make your case.