The most common opening hours for car hire companies at this airport are:
Sunday: 07:30-19:00
Monday: 07:30-19:00
Tuesday: 07:30-19:00
Wednesday: 07:30-19:00
Thursday: 07:30-19:00
Friday: 07:30-19:00
Saturday: 07:30-19:00
You'll find more details about the exact times during the booking process.
If upon arrival at Hua hin you wish to purchase additional services or must pay any outstanding charges, you must do so in the currency of Thailand, which is THB.