For your first month you have two goals: (1) Not to get injured and (2) to establish a routine (and be *fanatical* about this). 3 one hour workouts a week can make huge changes to your body if (a) you use that hour optimally and (b) you are regular and consistent in your training. Get a routine and DO NOT BREAK IT. Eventually you´ll have the discipline and instinct to know when you can. For now (first 3 months) be legalistic.
To start with aim for 40-45 mins a session. Gradually increase to an hour, but don´t do more than an hour. Work hard and with integrity, but don´t strain and compete. You don´t know your limits well enough for that until you have been training longer. Aim to do it RIGHT and not to try and look good or keep up with that guy next to you. He doesn´t care how many lb you lift. Really. He doesn´t give a fuck.
-Find a time that works for you (morning or evening, weekends etc).
-getting there and changed is half the battle.
-you can create an addiction to the endorphins if you try
-don´t make excuses. Do it.
-be realistic about what you can budget in time, but once you make the decision stick to it for a month. If after 4 weeks you decide you got it wrong you can change it, but you can´t change your commitment until then.
-don´t push yourself too hard in the first few weeks... just get there and get comfortable is enough. learn as much as you can. knowledge is most of the the battle.
We have all been through this. You are no different. just do it. report back.