Hahahahaha, WTF? If you spend more than a couple of days learning major scales, you're wasting your time. I learned major, minor and phrygian scales, and the relationship between relative and parallel major and minor in one 55 minute class period. After I got back from class, I went online to find out what the other four modes were, and I understood the relative and parallel relationships between all the diatonic modes in under a DAY.
After you understand those few simple concepts, learn harmonic minor, and the relative modes of harmonic minor. Don't even bother spending any more time with major scales other than for building your finger dexterity, which will be important when harmonizing over a minor lead.
In just about any type of metal, the two scales that you'll use the most are minor and phrygian, or harmonic minor and phrygian dominant.
Also, I've been planning on creating an instructional thread in this forum for a while now, so I'll add this to my list of threads to bump when I finish it.