Outlook autodiscover

I am going to migrate accounts to Microsoft 365 off of an old exchange server, but the exchange server will be running right up until the cut-over weekend. I am setting up the accounts right now. There will be 14 total email accounts. I have set up 3 and want to test a few things first before all accounts are created. I wanted to make sure I could set up an additional outlook profile in Outlook 2013 connecting to exchange in Microsoft 365. I cannot turn off the existing server until the cutover date, nor can I change the mx records. Outlook 2013 will apparently not read the auto-discover records. I have done numerous things to negate the local server, but isn't there a way to point to the autodiscover manually? Or setup manually as in the past?