[Although this slumber is only a simple session of meditation in which he familiarizes himself with the 'great' Corruption energy in his case, he shouldn't wake up before you reach him.]
"He stays dormant for that long?"
[The process takes a lot of time due to both the restricted ability of the artifact and the limited control that the demons' have over this space. According to my database, the Demons keep this state to pass the time till the target that has been completely converted into a 'Corrupted Puppet' makes its way to their location due to the puppet's natural instinct to reach the closest Corruption energy user to it.]
"So… in order not to mess up and leave early before the target is completely Corrupted, the demon goes to 'Sleep' and waits for the 'Alarm Clock' puppet to wake him up…? Isn't that simply too much of a time waste in the demon's case?"