I have a lot of experience in training, yet now I drink to much...such is life I guess.
I am a 'fast gainer' and fast loser too. One year I plumped up (divorce) and lost about 90 lbs in 3 months (5'11" went from 189 with < 10% bf originally: 240 then back to almost 150).
Within 3 months at the gym people notice a BIG difference in me, the first month is the hardest though, the first week painful.
Most people make the mistake of overdoing it and actually break down more than they are building up.
Most americans eat more protein than they need....your body can only process about 40 grams every 3 hours or so (about a deck of cards size piece of meat).
If you want to build don't do cardio....it breaks down the body too much (it is healthy though), and yeah 20 mins is all you need really (about 10 mins to warmup and 10 mins with your heart going), three times a week.
Personally I love going back to the gym all fat and bloated and having the guys poking fun at me....then watching as month after month they all back down until I follow them and one up them on all the weight they use.
I can still curl about 80 lbs with one arm (some one in a sports authority type store mentioned 'no one could curl that' so I did, my back pinched a little the next day though hehe)....even though I look like a push over 🙂