The documentation on CREATE EVENT is quite good, but it takes a while to get it right.
You have two problems, first, making the event recur, second, making it run at 13:00 daily.
This example creates a recurring event.
CREATE EVENT e_hourly
ON SCHEDULE
EVERY 1 HOUR
COMMENT 'Clears out sessions table each hour.'
DO
DELETE FROM site_activity.sessions;
When in the command-line MySQL client, you can:
SHOW EVENTS;
This lists each event with its metadata, like if it should run once only, or be recurring.
The second problem: pointing the recurring event to a specific schedule item.
By trying out different kinds of expression, we can come up with something like:
CREATE EVENT IF NOT EXISTS `session_cleaner_event`
ON SCHEDULE
EVERY 13 DAY_HOUR
COMMENT 'Clean up sessions at 13:00 daily!'
DO
DELETE FROM site_activity.sessions;