The lower limit settings aren't working

The lower limit settings are not working for our site. We have them set to 4 hours (the number 4 is in the field). In addition, customer are able to schedule an appointment any time of the current day, even a time that's already passed. This is the second issue we've had with this plugin, and it's costing us much precious time. Therefore, if this is not resolved ASAP we are going to be forced to request a refund and if need be dispute the charges. Please advise.