I think present research shows that 10 hours per week is the minimum required to achieve a body transformation in 3-4 months. 
Some recommendations:
1. "Body For Life" if you want a simple way to lose weight and gain strength. 
2. "Maximum Strength" if you'r already been lifting for a while and want to get stronger. This is system also has you challenging your own limits so that you feel certain sense of achievement instead of just "wow I look thinner" ... 
3. "P90X" if you like intense workouts with results.<p>I've personally done all 3 in the above order to pretty good results. After achieving the results , you really need to maintain a minimum level to keep it.