Sam 4-Heart Event Not Triggering?

[Capryus]

So, it's Fall 5, Year 1 in my game, and I've activated Sam's 2-Heart Event and his 3-Heart Event. Now I'm trying to get his 4-Heart event, but no matter what time of the day I attempt to trigger it, it doesn't work for some reason.

Is there some sort of buffer between events to keep them from all happening at once? Or am I not doing it at the right time? Or is the game just bugged?