I have five accounts on two battlenet logins, with one authenticator. Obviously three on one, two on the other. When logging all five at once, I find that I only have to wait about 30 seconds at the most to log in the next account. Sometimes I can get away with using the same number if I am fast enough. The sole reason I have the two battlenet accounts is to double my chances for Blizzard beta invites and I had two email accounts at the time.

What I do find to be a pain with the two battlenet accounts is remembering were all the alts are. I have org chart showing were everyone is at.