Substantial muscle growth can be achieved with 40-minute sessions 3 days a week, sometimes much less if done correctly. Muscles will only grow in size when they have fully recovered from the gym workout, then, and only then will muscle growth happen. If your goal is to achieve maximum muscle growth in the shortest possible time then there needs to be more rest days than actual workout days.

It's difficult for some people to believe that substantial muscle growth can be induced with only
2 or 3 days a week at 40 minutes a session, or less. It can be done and it is being done by many, however, there is a catch:

These "few and far between" gym sessions will have to be short and extremely intensive. More intense than ever, you have to justify your days off. You have to give your body a very good reason to grow bigger muscles. The sessions will be about what you thought you could not do, but somehow managed to do.

Eg: if you're lifting a certain weight and you know you can only get 8 reps, you will push yourself further than ever before and squeeze out another 2 reps of that weight, with the help of your training partner or someone else of course. You will need help with the last 2 reps but the idea is to execute a greater effort than you are used to doing, this creates the environment for greater muscle growth (all other things being equal).

Below is an example of an 8 Week "every other day" muscle building routine. It's an example of how short the training sessions should be. It can also be done taking 2 days rest in between training sessions. I am assuming that you have weight training experience behind you, and also that you are familiar with the jargon. If not, then I would not recommend that you push yourself too far until you have built up your strength and fitness level. You should always get the go-ahead from your GP or health professional before starting or changing any physical exercise program.

Warm ups are not included in the below.

Day 1:
Chest - 2 sets 10 reps 1 exercise. Use the same weight for your 2nd set.
Biceps - 2 sets 8 reps 1 exercise. Use the same weight for your 2nd set.