I am used to hearing the phrase “Nishtanu Hateva’im” regarding the third day after circumcision, per the Gemara, Rabenu Bachye Bereishis 34:25 (יגדל הכאב בכל מכה ביום השלישי), etc. So, we don’t heat up water on Shabbos, but who says the basic reality has changed?
I recently had a tooth pulled. The dentist told me to expect the pain to climax 3 days later…
Apparently, the science is unchanged, see here (thanks to Mi Yodeya!).