It spawns every 40 minutes to 2 hours. I don't know the exact time, but CC until you find it.

He randomly spawns once every half hour to an hour (I don't know the exact time).

Because every map in Maplestory only supports a set number of monsters, you'll have to kill a few to make room for King Clang.

Also, make sure you're at Florina Road: Hot Sand.

Same as above. You might not see him at first because he camouflages with the other shells on the hot sand map. You need to attack each shell to find him and then when his shell's hp reaches zero, you need to defeat his real form. However, he might not be there when you get there so cc or just defeat enemies or something until he does appear. Good Luck! ^_^

Hope this helps~ ^_^

King Clang spawns in Hot Sand the farthest map to the right apparently he looks different from other shells if you want to see a picture of it go to
http://global.hidden-street.net/monsters/mons6.php
scroll down till you see him. he usually spawns in a while, just cc or so to find him