When to start 2nd spec

[Ooshima]

One important thing: Cross class skills do NOT have levels. The first slot is always available, second slot at level 10, Third slot level 20, etc. The cross class skills will scale appropriately.

Should also mention that 10/20/30/40/50 are applied to Jobs (with your Job Crystal) - prior to level 30 and having your Job Crystal, IIRC you have one cross class slot every 5 level, up to 10 - so don't be afraid to use them if you happen to unlock your a lot more cross class skills (without your Job Crystal, you tend to have more access to a wider variety of cross class skills to use).