Different cutting bit run times

Could anyone explain to me why the carve time on my 30 degree detailed vbit is 9 hours, and when I change it to a 60 degree it is only 4 hours.
Thank you.

The 30 degree bit needs to carve deeper, thus more passes. The smaller the number the deeper the cut. V Carve cuts as deep as it needs to create cutout path between the lines .