I am wondering how second and third string players develop. Does it happen during practice or does it require game time?

I am having a issue whereby playing as GM only, that my second/third string players are not seeing playing time during the preseason (coach controls the depth chart and play calling). I want to make sure that I will have players develop during their careers even though they may not be starters during year one or two.

Thanks,

Yes, they are added to a default training schedule that helps them improve throughout the season.