Let me share some additional details about removing the line item on your transaction, lynnrob.

You're not missing anything.  In the new invoice lay out, once you click the Unlink and delete (Yes, unlink it) option, the time activity will be removed from the invoice. However, if it still will stay in the Suggested transactions panel. You can choose to add it again the next time you create an invoice for that customer. See the screenshot below for your reference:

However, if you delete a line item from an invoice (without unlinking the billed time), we can remove the Billable time from the linked transactions. Just click the trash icon beside the line item and you'll receive a prompt message that you'll have to unlink the Time Activity. This removes all other lines associated with this transaction. Otherwise, removing the Billable time will let you keep the Time Entry. 

You can also check out this article to learn more about how billables work in QBO: Enter billable expenses. To learn more about tracking and invoicing your billable time in QBO, check out this article: Enter billable time by job in QuickBooks Online.

In case you have any further questions about your billables and invoices, you can always tag me in your reply. I'll be around to help you. Have a good one and keep safe!