Magic Calculated Before/after Casting Starts?

I feel like this is probably such an elementary thing, but I have never been able to find the answer and then get bored looking and forget to come back to it.

My question is, when calculating all that fun stuff that comes with casting spells (Magic accuracy, Magic Damage, etc.), when does the calculation actually take place?

Should I be macroing in equipment BEFORE I start casting, or does it just need to be equiped before the spell shoots out finally/hits the enemy.

I feel like I'm going to get attacked for asking such a simple question that probably has the answer all over the internet, but I couldn't find it anywhere for the life of me and am tired of wondering. [Please assist][Thank you]

Damage and accuracy is calculated the moment the spell hits so as long as your M.acc, MaB, and INT or whatever else you have for damage is equipped before the spell hits your target it will be in effect (Same for haste/fastcast for reducing recast timers). If you want Fast Cast (for faster spellcasting) or any kind of gear that has casting time reduction it needs to be on before you start casting.

Edit: mistake lol, hit quote instead of edit and posted again.