The key decision happens right after the Relay event/Ari stealing the coins and panties, but to play it safe I would play since the ending of the footjob scene, which is where 0.4.2 ended.
When skip-to-day feature comes out, this should be easier to manage as the idea is to allow people to jump to specific points and re-make all the choices up until that point.
The more the NTR/NTS haters lash out and hate the game the more it reinforces that idea that the updates are going in the right direction, can't wait until 0.6.x comes out