Can I get the car earlier if I arrive earlier ?

Yes, but you have to do it in advance when you return the car

They calculate it by the day. For example, if you pick up the car at 9 a.m. on the 14th and return it at 9 a.m. on the 15th, it counts as one day. If you return it at 10 a.m. on the 15th, it counts as two days. Similarly, if you still return the car at 9 a.m. on the 15th, but you pick it up at 8 a.m. on the 14th, you will also have to pay for two days.