Ideally, the active game play time required to craft the product would be approximately 8 weeks. This means the final product would be quite expensive and be reserved for "extremely important" enchants/items.
I'm not sure what is active game play for you.... is it full time grind or simply a couple hours a day ?
In any case I feel like 8 weeks is a bit overkill since you will probably need several protection potions prepared before attempting to enchant since you're likely to fail enchanting one or few times which would blow up the protection after each fail.
If I want to enchant a rank 5 enchant with protection potions, I would probably prepare at least 3 potions before even attempting the actual enchantment which would take me 24 weeks (assuming I'm making them alone), almost 6 months before even attempting an enchantment. And that's when we are already high level to be able to make the potion in the first place.
Two to four weeks seems more reasonable to me. Now, that's my personal opinion.