What you want is called an "event". Here's a potential definition; your needs may vary.
CREATE EVENT `zero_my_column`
ON SCHEDULE
EVERY 72 HOUR STARTS '2015-07-13 00:00:00'
ON COMPLETION PRESERVE
ENABLE
DO BEGIN
UPDATE mytable SET counter = 0 WHERE counter <> 0;
END
There's some configuration work to do to ensure your MySQL server will run this event correctly.
This is the actual update query.
UPDATE mytable SET counter = 0 WHERE counter <> 0;
Notice the WHERE
clause. That prevents redundant updating of rows that already have a zero column value for counter.