I get asked regularly how long someone should ideally exercise for.
This depends on the fitness programme being undertaken, how regularly it is followed, what the objectives of the workout are, and how much time the individual can give to the programme.
The last part of the above is more important than you might imagine!
In broad principle, however, it is perfectly possible to undertake a demanding, effective workout in 45 to 60 minutes, inclusive. It all depends on how you combine which exercises during the workout, the pace at which you train and how long you take between sets.
Target the major muscle groups in your workout plan before you begin, know what you will be doing before starting, deliver each set with attack and you can finish on time, plus get the results you need.
Attitude and expertise are important, as is focus (something which I cannot stress enough), as Joshua demonstrates in the video, above.