I found the option to default the personal email account under the My Profile options for the user.

I'd guess 20-30 minutes but the user was in the same room, so it was easy to setup the MFA.

We set it up for one user. My only compliant so far is that it doesn't override the system default email account (that I can find). So the user has to...

You can also look in the EPApproval table. I don't have approvals turned on for payment, but EPApproval stores the Bill Approval prior to releasing.