I have some time on a C402-C.
The first question though is does the one you are going to fly have a vortex generator kit? If so, it raises the MTOW from 3107 kg to 3270 kg. The MZFW is 2955 kg in either case.
So using the MZFW as max payload you can carry either 315 kg or 152 kg of fuel, 437 litres or 211 litres respectively.
Maximum fuel is 780 litres and most C402-C have a block rate burn of 130 litres/hour although the one that I have flown burns closer to 140 litres/hour. At 130 litres/hour and 437 litres you are going to get 3.3 hours of noise before there is silence from everything except the pilot, for 211 litres it is 1.6 hours.
On the aircraft I flew I flight planned at 170 knots which for the most part is reasonably accurate but I also fly in a part of Australia where wind forecasts are accurate only when there is a blue moon. So with leaving a bare 45 minute reserve you are going to get a range of about 425 nm and 136 nm respectively.
Please treat as a guide only as there is quite a difference between particular aircraft. If you are going to be a pilot of one they are a very nice aircraft to fly, Cessna finally got rid of the idiotic fuel system they borrowed from the 310 and simplified a lot of the systems. Engineers on the other hand hate them because of the difficulty in getting to a lot of the bits.
