I give them a full season, how I do it is if there academy players with lower skill value I play them in the cups or as cover when short, if they gain skill quickly I keep them if they are constant failures I get rid, as for buying players heres something for all you lot, I NEVER check his game ratings!, I buy for position and skills only, I make the judge of them playing in my team, I try to keep the 18/19 year old best I can.