Glad to see you here, @MichaelQAmera.

There isn't an option to change a label from the invoice page. However, you may consider customizing your invoice template that you're sending to your customer. This way, you'll be able to change the column for QTY to HRS.

Here's how:

1. Click the Gear icon.
2. Select Custom form styles.
3. Choose Invoice from the New Style drop-down arrow.
4. In the Content tab, click the second Pencil icon.
5. Click Edit Labels and Width.
6. Change the Quantity label to "Hrs."
7. Hit Done.

You can also make this template as default.

Here's how:

1. In the Custom form styles page, locate the invoice template.
2. Click the drop-down arrow under the Action column.
3. Select Make default.

Here's an article that will help speed up your work in managing your invoices: How to create a recurring invoice?

Don't hesitate to comment down below if you need further assistance. Have a great day.