Adding a Date Stamp - Original Time Stamp and Modified Time Stamp

I'm having a hard time putting this into words, so I'll try to make it simple.

I have a list with cells (D1 thru J1) and (L1 and M1) and (R1 thru W1) empty.

If one or more of those cells becomes populated, I want today's date to show up in cell K1 (activity date) and n1 (entry date).

If any of those fields from (D1 thru J1) and (L1 and M1) and (R1 thru W1) is modified, K1 (activity date) will show modified date. N1 (entry date) will NOT change

 
Yes, the user could enter the date manually, but apparently that's too difficult for some people.

 

Any help would be appreciated!!!!