Timer for charger?

We have a store with a type 2 charger for the use of our customers for free. So far it has worked well for everyone but occasionally someone will leave their car plugged in overnight or for a long period during the day.

We would like to continue to offer the use of the charger but is there some way that we can fairly easily, and at reasonable cost, install a timer to limit charge times to an hour or two? Thanks!