Need help programming in excel

Trying to track re admittance of patients:

I created a formula in a cell that deducts one date from another. I'm trying to create a cell that will then take that data and if it's less than 30 days or greater than 0 days it comes back with a Yes output. AND or I want it to only populate a YES if that field is <30 days but if there is no data in the field to just leave the cell blank.

I've tried the IF function and can get it to calculate the YES but when I tried to figure out how to get the cells with no data to read blank I'm STUCK.