To get more training hours faster in Career mode, do not sign long term contracts. Just sign one year contracts and do not renew after the season. Find a team that is weak in your position (or stay with your team) and go to spring training. If you are a position player, you will receive an extra 600 to 900 hours if you simulate, if you want more hours, play the games. You will make the team almost certainly. If did not make the team, you probably would have started the season in the minors regardless and not signing will not hurt you but only help.