Mark's answer is correct.
He was only showing the WHERE part of the query.
The full query would be
But Keleth's answer should have worked, too.
DELETE FROM import WHERE DATE_ADD(Timestamp, INTERVAL 35 HOUR) < NOW()
Part of your problem may be that timestamp is a reserved word in MySQL. You really should try to avoid using reserved words as field and table names.
If that is the problem, though, you can just enclosed the name in BACKTICKS -- the ` character that shares a key with the ~ tilde.
DELETE FROM import WHERE DATE_ADD(`Timestamp`, INTERVAL 35 HOUR) < NOW()
DELETE FROM import WHERE `timestamp` < NOW() - INTERVAL 35 HOUR