Like the previous question, this again depends on how fit you currently are, what goals you have set for yourself and how much time you have to devote to working out. For some people it may be best to schedule three hour-long workouts per week, while others may find it more convenient and beneficial to train 5-6 days per week - but for only 30 minutes. In other words, it is best to think about how many total hours per week you will spend in the gym, and then to decide how best to spread it out. Another important point to consider is quality of time and not just quantity. Someone who is very dedicated and focused to his/her training can often get far more accomplished in just 30 minutes than one who is there for an hour, but constantly distracted by his/her phone, chatting with others, and/or watching rather than doing.