I reckon a nod and a smile (maybe not too much of a smile if it's public toilet in a park at night...) never goes astray.
I didn't know 3:15 was "that time of the day". Were you not curious to know what he meant by that Snuffy?
The only hitch is starting a long conversation that then becomes very awkward if one person finishes their ablutions before the other and is obliged to hang around the toilets purely to avoid walking out on the conversation.
And never start chatting if you suspect that performing said ablutions may leave you grunting or short of breath!