Garrett - Welcome to our forum
From your post, I have interpret the following situation :
You are trying to create multiple work orders and want to perform this task all from the invoice screen. You are entering several Service Date items on the invoice screen and want those service dates to become work orders and allocate them in the Method calendar.
It is not possible to tie an Invoice Service Date action to create an event on the Calendar. The workflow for the Field Services application should always start with an Estimate or Work Order. Once you convert a Work Order to an Invoice your service date field will be populated with the Work Order start date.
You can also perform recurring Work Orders by selecting Recurring Dates tab and choose your desired set of dates.
Please let me know if I can be of further assistance.