Kevin, I'm assuming that tasks are removed from the table as they're performed and that you may need to "catch up" a few tasks if processing takes longer than a minute. That's why you used the <= att_min, right? If so then you may lose tasks if processing crosses the hour boundary- e.g. starts at 10:58h and the sql is not run again until 11:00h meaning you've missed any task at 10:59h. you could check for that by

SELECT att_pk;
FROM AutoTask;
WHERE HOUR(DATETIME()) < att_hour or ;
(HOUR(DATETIME()) = att_hour AND;
MINUTE(DATETIME()) <= att_min)

though you may still miss tasks if processing crosses the day barrier- e.g. runs at 23:58h and not again until 00:00 the next day.

Also, if it's possible you might have tasks from several minutes at once, you might add an ORDER BY to ensure that tasks are done in their intended order.