Warning - I can't get to my MySQL instance at the moment so you may not be able to just copy&paste this ...
Try selecting from your database like this ...
select TIMESTAMPDIFF(SECOND, receivedtime, requesttime) as difference, TIME_TO_SEC(sla) as slasecs from table
and then you can do your
if [difference <= sla]
{
show meet
}
else
{
show don't meet
}