Be very aware of the "24 hour clock rate" most rental car companies use when charging you.
This means if you rent your car on Wednesday and return it on Thursday, you are charged for one day only if you return it within 24 hrs. You are usually charged for 2 days if you return it more than 27-28 hrs after picking the car up.
The policy for most companies is that an hourly rate is charged for the first 3-4 hrs after 24 hrs. Returning the car after the hourly rate period means a whole extra day is usually charged.
Be aware that this procedure can vary from company to company and that some companies use a calendar day billing policy wherein you have until midnight to return your car before being billed for a full extra day.
Ask the company BEFORE you drive away what their policy is and whether or not they offer a "grace period." My experience is that they might offer 1 or at most, 2 hours (2 hours may be pushing it). In your case, they MIGHT let you go until 10 A.M. But do not assume this is the case. ASK FIRST.