When does the training your players receive affect their abilities? I thought I read somewhere that you have to set your training by friday...
The training which you have set by the Friday update is what you get. This means that you can change the training, e.g., based on minutes, during the week as many times as you like.
I am assuming that you would see a green upward arrow next to the stat you trained if it actually worked or not correct?
There's a green arrow, when you get a skill pop, i.e., when the skill level changes. Your player may need several weeks of training to get a skill pop. However, each training improves the player although there is not necessarily any visible improvement.