Minutes instead of Hours on "Invoice Created" Email Template?

[ETT]

I need to change the text in the "Invoice Created" Email Template.

 

Actually, I need to modify the Available Merge Field "{$invoice_html_contents}"

 

I need to change the word "Hours" to the word "Minutes", since I have some services that are charged per minute rather than per hour.

 

I've looked and looked, but for some reason can't find where to make the change.

 

Please help!

 

Thanks in advance.