We know there are 60 seconds in 1 minute, and 60 minutes in 1 hour. We also know there are 24 hours in one day. If we multiply all of those, we end up with 86,400 seconds in 1 day.
60 seconds in 1 minute x 60 minutes in 1 hour x 24 hours in 1 day = 86,400 seconds in 1 day