Can I set up a voluntary deduction with an amount withheld per hour?

Welcome to the Community, @PSM1.

I'm here to shed some light on payroll deductions.

In QuickBooks Online, we don't have the option at this time to set up hourly deductions. 

However, you can add a payment type to the employee. I'll submit feedback for you on this, and hope for it to be in a future update. 

For information on updates coming to QuickBooks, take a look at The QuickBooks Blog.

Learn how to set up voluntary deductions in your online Payroll account.

Voluntary payroll deductions are amounts subtracted from an employee's net pay to cover the cost of things such as employee-paid benefits offered by the employer, or general deductions like a charitable donation.

Note: Pretax deductions must come out of a taxable wage item. They will not deduct from a reimbursement type wage. 

For the tax-ability of each deduction, see Supported pay types and deductions explained for more details.

QuickBooks Online Payroll

1. Choose Workers, then Employees.
2. Select the employee's name.
3. Click Edit ✎ next to Pay.
4. In section 5, select + Add a new deduction or + Add deductions.
5. From the Deductions/contributions ▼ drop-down menu, choose New deduction/contribution.
6. Pick a Deduction type and Type from the small arrow ▼ icon.
7. Enter Provider name (appears on a paycheck).
8. From the Amount per pay period ▼icon, choose $ amount or % of gross pay and enter the amount or percentage, do the same for the Company-paid contribution as applicable.
9. Select OK, then Done.

You can add the same deduction you've set up to an employee to other employees by assigning it to them. 

If you have any other questions about setting up deductions in QuickBooks Online, just reach out. I'm only a reply away.