At my dojo, we learn about atemi around day 1. (maybe day 2
) Atemi during PRACTICE is different from street usage, however.
Take for example a yokomenuchi strike (strike to side of the head) : as the attack is coming in toward the nage, uke also brings their OTHER hand up to block/absorb any possible counter strike. Failing to do this at my dojo can pretty much guarentee missing the atemi and expose how the uke is vulnerable.
Protect yourself at all times! Move your feet and don't expose the family jewels... get your hands up and expect a blow to the head or chest... GET OFF LINE!! ( I know, I know... I'm still working on this one too.
As for atemi to pressure points on the arms and such, be relaxed and flexable and ready to move. They don't HAVE to hit you hard, but if they hit you right... it doesn't matter that much now does it?