Correct time for gym workout - morning or evening for better results? i have been told that testosterone levels are high in the morning.

Depends: Yes, testosterone levels are highest around 0800, but there has been research suggesting that weight training in the evening is better. Truth is, time of training depends on your goals. For example, I often recommend high intensity cardio on an empty stomach first thing in the morning. Such training would not exceed about 20 minutes, so you do not need to worry about getting "catabolic".