[Miller]

Using Blazing Sol with 2/3 charges isn't useless, it still locks your Solcharges until the end of the turn; which lets you double up on 2-3 cost Solcharge skills.

I don't think I like either of these options. If you increase the duration, you're giving already really powerful buffs another turn (4 turns of 10% ele pierce, 15% mag dr/phys dr or 2 stacks of Combination Fighter); if you make it activate once you start using it, Wall gains more value if you go first.

If it had to be one, I'd go with B).