Trying to assign a user in linked account as alternate host, but instructions fail

The Scheduling privilege and alternative hosts page says we can add alternative hosts and assign scheduling privileges to other users in the same organization, including users in sub-accounts. I'm following the instructions to enable this account-level setting, but I can't get it to work. 

I have successfully linked my two Pro accounts into one organization. (screenshot)  

(I am slightly confused because the main instructions say "link the master/sub account in IM settings" but the how-to page never actually takes me to the IM settings.)

After linking, I follow the instructions for enabling the alternative host setting. When I get to step 5 in the instructions, though, it tells me to change settings that aren't there. (screenshot) 

If I try to assign an alternate host to a meeting anyway, I get the error that the email can't be found. (screenshot)

(I am trying to use the owner of the sub-account as the alternative host for a meeting in the master account.)

Has anybody else solved the problem where step 5 on the Scheduling privilege and alternative hosts page tells you to edit some settings, but those settings aren't there? Maybe there is a problem after all with trying to use the alternate host setting with organizations?

(I tried submitting this to support, but say they are "unable to respond to the open ticket at this time".)