SharePoint 2013 Workflow dates

I have a "Start Date" column that is a single line of text and displays a value from an InfoPath date control .
In a workflow, I need to compare that value with "now" and if it is greater than or equal to "now" initiate a task.

The Now workflow variable gets it's value at the start of the WF as follows:
Set "CurrentTime" to Current Item:Modified and has the value in the format m/d/yyyy hh:mm A.
The "Start Date" column show the date string as yyyy-mm-dd

As a result of these differences, they never compare equal.

So,  I tried to build a Year variable, a Month variable and a Day variable from the Current Item:Modified column as follows:

1. Copy from Current Item:Modified, starting at 1 for 4 characters (Output to Variable:CurrentYear)
2. Copy from Current Item:Modified, starting at 6 for 2 characters (Output to Variable:CurrentMonth)
3. Copy from Current Item:Modified, starting at 9 for 2 characters (Output to Variable:CurrentDay)

Thinking I can build a string in the format yyyy-mm-dd and then use that for compares.  I don't find a way to build this string nor am I sure if my approach will work.

Any advise on this would be appreciated.