In QB Desktop I could record an employee's time by job and it would then calculate the payroll expense for each job. How do I do that in QB Online?

You can definitely do the same with QuickBooks Online, rachelwebb03.

Simply turn on the copy hours from employee time sheets function in the Payroll Settings. Then, QuickBooks will automatically syncs the hours entered from timesheet in to employee's paycheck. When payroll is approved, that's the time we'll account them in the payroll expense account. 

Here's how to turn it on:

1. Click on the Gear icon.
2. Select Payroll Settings.
3. In the Employees Overview, click on the Time Sheets link.
4. Choose Copy hours from employee time sheets.
5. Click on OK.

To enter employee's time by job:

1. Click on the Plus icon.
2. Select the Weekly Timesheet or Single Time Activity. 
3. Select the employee name and the period. 
4. Choose the service or account, select billable, choose the job.
5. Enter the hours.
6. Click on Save and close.

The hours entered from there will show when running payroll for that pay period. I've got you some great resources to help you some more:  

• How To Turn On and Set Up Time Tracking
• QuickBooks Online Payroll Time Tracker

Please let me know if you need anything else. I'm happy to help.