how to increment date automatically every 2nd friday of the week at 11:30am (EST time zone) ?

I want to display 2 dates on the webpage like
Start Date:
End Date:
I want to save a static date in the database, my table is like this:
Tbl_Date
id           int
start_d    datetime
end_d     datetime
Now once I manually save a date in these columns (start and end), I want 14 days to be added to both start and end date on every 2nd Friday at 11:30am according to Eastern Standard Time and the new dates values should over-write the original start and end date.
How to do this ? Please HELP ME with the code.

...