How much time and effort depends on a person, but for a young genius like Ingrain Hollow, it shouldn't take that long at all.
About a decade or so from my estimation, but that is just an estimation.
If his latent potential is great, it would take less time, and from the way Ingrain had managed to resist a Tier 4 Spell despite his age, his latent potential is fairly high. His mental strength as well, I suppose.
Of course, Ingrain also needs to understand or at least comprehend Runic Text in order to make sense of the Void Devourer Manual. This is because the manual is compiled with Runic Text, and that is due to my personal preference.
While I can compile it in Minasian, it would not be the same, as there are powers within Runes, and if a manual is written entirely in Runes, it can be considered as a Grimoire.
Grimoire are basically magic textbook, allowing the wielder to cast or activate any spell or instruction within the pages at the cost of their own mana. As such, it allows inexperience mages and the likes to cast spells that are beyond their current power level.
In addition to that, I can impart my will and spirit upon a Grimoire, making it somewhat sentient. And a sentient Grimoire is much more useful than a simple manual, at least for what I have in mind.
Once I finish compiling a Void Devourer Manual, I have a look through it to see whether it is correctly compiled or not, and I must say that while it is not the best manual to transform ordinary mages into Void Devourers, it is still quite good.
Good enough for Ingrain, as I do not need a manual to become a Void Devourer. Everything I need to be a Void Devourer is within my mind, and through that, I can always create more manual manually if needed be.
The final touch is imparting my will and spirit onto the manual, turning it sentient. I also need to store some mana within the Grimoire just in case. Having access to mana, the Grimoire can cast magic while not in the possession of others.
That is always a good thing.
I sell the completed Grimoire to the Shop System to create a record since it will save time in the future, as Ingrain will not be my only disciple. More disciples at my command allows more thing to be done.
"Master Kilian! Master Kilian!" a voice echoes in my mindscape, and that is the cue for me to wake up and return to the outside world.
And once I slowly open my eyes, I express my confusion just like everyone else already have. While no one can remember what had just happened due to my spell, they are aware that there is a gap within their memory.
"W-what happen?" I question and look around the room.
"We somehow all lost consciousness," a boy speaks up while checking himself, making absolutely sure that nothing was taken from him. His female companion is doing the same. And once they both realize that nothing was stolen, they exhale a faint breath of relief.
"And who are you?" I add.