Have an analog clock handy. Show your child the different hands on the clock. Point out the difference in size between the minute hand and hour hand. If there I a second hand, also point out the differences. Show your child how the minute hand moves from one minute to the next in 60 seconds. Clap 60 times in a minute to show how quickly a second passes. This is also a fun way to reinforce the concept of a second. Compare how quickly the minute hand travels once around the clock to the hour hand. The minute hand goes from the twelve to the twelve and the hour hand only moves from one number to the next.
To explain the concept of an hour, compare it to a task that may take an hour. Ex: Having dinner, getting ready for bed, etc.,
Finally compare an hour to a day. Explain that a day is when the sun comes up in the morning until they go to sleep and wake up the next day. Tell them that there are 24 hours in a day.