For me, for about a year and a half, it used to be always worse day 1, then slightly better day 2. But nowadays, in my third year of POIS, I feel almost no symptoms on day 1 and it all starts on day 2. I've been experimenting with various supplements, now also with garlic.
There was a statement in one of Dr. Waldinger's papers that the occurrence is pretty stable within a man (and varies quite a lot across men); this is not quite the case for me, as I've been experimenting.
It is often hard to tell which day it is also because I get symptoms after just pre-cum (e.g. if I look at a beautiful girl on the streets and pre-cum a little bit, without ejaculation or orgasm).
This week, I was doing another experiment: try moderate physical exercise on day 1, despite the fatigue. I tried and felt great. Tried also moderate on day 2. Again I felt fine. But then I just woke up on day 3 with some of the symptoms. But I also had some precum this morning.