How do ampules work?
Viewing post in My Maid Dreams of Electric Sheep comments
The sleep one is pretty immediate if I recall but the only real use for it is to unlock the sleeping sex scene. The one that increases arousal isn't immediate and takes about a week of you not having any sexual interactions with Ako to work and unlocks the rape scene where Ako being unable to control her lust any longer starts riding you in the middle of the night and also unlocks an optional punishment blowjob the following morning.