To use the Fain Immortal Peach Lily, one must keep it in their vicinity and cultivate it for a maximum of 20 days. For many, it would help elevate their cultivation base in just a week or so, but there were instances where it was known to take up to 20 days, depending on the person's Battle Power.
It took Alex nearly 26 days to break through using that flower.
The flower when left nearby during cultivation, assuming no other being cultivated in the vicinity, quickly gathered Qi from the surroundings and sent it directly to the cultivator, which helped improve all of their physical aspects, getting them ready for the next breakthrough.
What usually took Alex 10 years to improve, here he was doing it in 10 days. He could feel his body refusing the 'aid' by the end of it, and if he were to do it again, it likely wouldn't work.
