If/Then Time Statements

I am creating a button to determine if something was completed early, on time, or late.  

The fields I will be working with in this formula are: 'Quoted Completion' and 'Timeliness'

When the button is clicked, I want to update a dropdown named Timeliness. The options in Timeliness are Early (1), On Time (2) and Late (3).

My conditions are:

-if the completion time ( now() ) is less than 15 minutes to the Quoted Completion, I would like to mark Timeliness as Early (1).

-if the completion time ( now() ) is greater than 15 minutes or 1 minute before Quoted Completion, I would like to mark Timeliness as On Time (2)

-if the completion time ( now() is equal to or beyond the Quoted Completion time, I would like to mark Timeliness as Late (3)

I know I would need to use if then statements, but I am not sure how to do this entirely.