At what point did you start endurance monster dwellers?

When I was at around 40 dwellers, I read up on SPECIAL and learned that for endurance, it actually matters to increase it before levelling up. Now I'm at 62 dwellers, stopped recruiting (well, mostly "procreating" - radio station only netted me 1 or 2 of my 62 dwellers despite having it since availability), and have 18 monster babies in the fitness center, most at L1 and all soon at 10 endurance. Other than that I don't have too many training facilities. 2 rooms (4 dwellers) each for strength and agility, 1 room (2 dwellers) for all the others. The non-endurance dwellers I kept rotating in those until all had at least 2 of each stat, now I'm rotating specialists (i.e. keep food producers rotating in agility, keep power producers rotating in strength training). I might to another round of general rotation when the endurance babies are maxed, to increase stats for parents.
I feel I'm kinda late to do so, but I'm curious at what point all of you turn up the endurance training and what's your approach to endurance and training your dwellers in general?