How strict about car rental companies pick up time?

I rented a car for a 1 pm arrival time. Since I made the reservation, the airline changed the flight time to arrive after 3pm.

It is also a question of different flight. Should I change my car reservation, or Company Rent do not care about a difference of two hours?

Only if you know a "reservation" is not a car warranty is just a "head up "to the rental company you probably like a car that day. If you join their frequent renter club free (though not often), usually maintaining a car for you, but if you arrive late and do not talk about this, then you can not get the car you reserved.

If you have given your flight information, so your flight arrival time changed. All car rental companies are related to reservation systems of airlines' flight numbers and arrival times. There will be no penalty for being late because they can charge you for a car he did not.