With the half hourly rate engine, you can charge for each 30 minute period of a rental.

The rate you set against the product is the leading rental period, i.e. the charge for 1x half hour. 

The minimum number of half hours to charge.

Keep in mind that if you enable chargeable days on an opportunity, Current will ignore the minimum rental half hours.

Use leeway minutes to add a grace period or tolerance to the end of a rental. 

For example, if a rental that starts January 2nd at 11am and finishes on January 2nd at 12:10pm then the total rental period is 1 hour and 10 minutes. This is considered three half hour charges. However, if you set 15 leeway minutes then the same period would be considered two half hour periods of rental charge as 10 minutes is less than the leeway minutes.