Understanding the game, understanding the math behind the game and understanding the psychology of the game could take a few months or a few years depending on how quickly you pick it up.
But...
You can be the best trained player in the world and still lose money. The one thing you need more than anything else in poker is a good run. You need a lot of days where the cards fall right, the fish bite well and the river treats you kindly. When you have these days having good skill makes them a lot more profitable.
If you're having bad days, bad week or bad even months then all the skill in the world won't make it better. These are the days you rather go fishing, read a book or watch some movies. If you must play then play at very low stakes to minimize losses.