With the hourly rate engine, you can set up a simple hourly charge. This is generally the price x quantity x hours. 

For example, 2 x product at $10 for 5 hours would be $100 since $10 x 2 x 5 = $100.

The minimum number of hours to charge.

Keep in mind that if you enable chargeable days on an opportunity, Current will ignore the minimum rental 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 two hour charges. However, if you set 15 leeway minutes then the same period would be considered one hour period of rental charge as 10 minutes is less than the leeway minutes.