Your spinner sounds like the VinylStack unit; its the only one I know that can spin that slow - 0.13 rpm. You can spin too slow. Depends on the tank power and temperature. I recently assisted someone who likely damaged a record, but he also allow the tank temp to reach about 125F.
I generally recommend 0.3-0.6 rpm and an even number (no factions) of rotations, so the record sees uniform exposure. 25 min may be a bit long. But this can be affected by how many records you are cleaning at-once and the tank size. General rule of thumb is to space the records about equal to the wavelength, so for 40kHz, 3/4-1 inch is about right.