I was also having trouble finding the "percentage of time I used for this business" within the Turbo Tax Online version, however, finally found it! Posting to help anyone else in the amazing thread.
The online version forces you in the "new rental property" flow which limits your responses as mentioned above. If you delete/tap trash icon for the New rental property line, then add a new asset, you will see the options that will allow you to entry the percentage of time used for this business.
