Halo 3 skulls question? Time it takes?

[balrr4life]

Ok, i know where all the locations are (based on guides and videos) but how long would it take to get all 13 skulls after beating halo 3? and how long if u havent beaten halo 3?
~THANKS

 

[Crash C]

You have to start from the beginning of each level and play through for them to appear, also you can't play on the easiest difficulty. So some levels take longer than others. But I did it in about 1.5 hours. Just quit out after getting the skull.