This is how it works:
After you talk to Nightly, Activate the statue. This causes it to "speed up time" so Rousing goes up fast
If you activate it again, maybe by accident, its works as a toggle. The Rousing is going down instead. Not what you want. Toggle it back again by activating
If you leave early or fall off, the statue will sink back down. You just start over. Nightly repeats instructions
If you stay near the statue, your Rousing reaching over 95 will trigger a Spontaneous Orgasm.
This is what completes the quest objective and progresses the quest
The objective will show complete and the description updates
Once the objective is completed, Nightly will show up again to talk to you, when you head down... either going down to the center of the platform room, or trying to go though the exit if you happen to fall off the platform due to your massive orgasm