Despite being exposed to 700 degree temperatures (even for seconds) Riddick is shown to be completely uninjured when he is dragged into the prison's hangar. He should have had at least second and third degree burns on his outer skin.
In the scene on Crematoria where Riddick is going to kill the guy with his "Tea" cup, he is obviously drinking something out of the cup. The final sip does not show him consuming the entire contents, but when he turns it upside down, not even a drop is left.
When Kyra removes the cup that Riddick used to kill a guard on Crematoria, the cup has a badly broken and jagged rim and its handle is attached about an inch below the rim. In the next shot where the cup is completely visible, the cup's rim is less broken and jagged and its handle is attached at least two inches below the rim. The cup she places on the rock appears the same as it did when she first picked it up.
After the Imam is killed, Riddick finds the Imam's tooth necklace on the ground. When we first see it there are small drops of blood around it. But only a few seconds later when Riddick goes to pick it up there is now a large half moon shaped pool of blood next to it.
A planet that has a literal 1000 degree (-300-700) difference would have to be extremely close to its sun, and have a barely existent atmosphere (Our planet Mercury has these same characteristics). Therefore breathing would be very difficult, if not impossible especially for running and climbing great distances.
When Riddick is scanning by Quasi-Deads, the one of them whispering "scanning fresh memories". In first row was found thoughts about young Jack, but those memories are 5 years old, not fresh. Much fresher memories (couple hours old) are about meeting with Aereon in Imam house, which was revealed by Quasi-Dead later.
Despite Crematoria having both a dense enough atmosphere to support human life AND 700 degree temperatures, there are no hurricane force winds that would exist in such an environment , especially when the temperature was transitioning from hot to cold.
After Riddick is left on Crematoria by the Necromongers he takes shelter in a garage. Because the planet is quite obviously devoid of any humidity at all, the thin atmosphere does not transmit heat. Therefore, all shade on the planet, including the "night side" (the half of the planet that is in its own shadow) is much cooler. A similar effect can be seen in desert areas of Earth. Ironically, the extremes mentioned mean that the garage actually would require heating of its own to keep the occupants alive.
After Riddick kills the first inmate with his tea cup and threatens the second one with his can opener, the remaining two haul their dead comrade out but it's not the same guy. It's actually the guy killed by Kyra earlier in the scene.
When the ship carrying Riddick is on approach to Crematoria, they're all just fine with the sunlight entering the windows. But once they reach the surface, suddenly the sunlight bothers them. The sun would have felt much, much hotter before they entered the atmosphere, it wouldn't wait until they reached the ground to start burning them.
The danger of Crematoria's heat is inconsistent. It kills one escapee instantly, doesn't burn Kira or Riddick (even when he's knocked out on the surface), and kills the necromonger who saves him after he takes 20 steps into the heat.
Water boils at 212F so at 700F all the water in the canteens would have been vapor once Riddick opened them. It would not help him stay cool enough to go in the sun. Even then Kira didn't get soaked in water, yet she didn't get burned.
Crematoria has no vegetation on the surface, due to it constantly being "wiped clean" by the suns heat burning away everything in sight when the planet rotates/orbits the local star. It would be considered a "dead planet", meaning no life of any kind. As a result, there would be no oxygen for anyone on the planet to breathe.
When Riddick is crouched on a perch looking up at the Necromongers entering the atmosphere of Helion Prime, the digital addition of the 'shine' of his eyes doesn't match up with his eye and head movement.