He mentions that he's running it in an air-conditioned studio, so presumably if the unit's datasheet lists an environmental range warmer than that, it has plenty of cooling headroom in this environment.

The last rubidium oscillator I played with, had to heat the vapor cell within the physics package, but then prevent that from overheating the rest of the unit, so it specified mounting to a heatsink. There was no heatsink recommendation given, just a certain package temperature as reported by sensor value X in the diagnostic data page. Get below that and you're golden. Get too much below that and you're wasting extra energy in the heater. Which is harmless, it just drives power consumption up.

So depending on how the unit's thermals work out, a slightly less aggressive fan may end up being mildly beneficial.