First off, yes this has probably been covered a million times, but it is a GOOD question, and you used above average wording, spelling, grammar, and punctuation. Since I can't give you a cookie, I'll answer briefly to the best of my abilities.
General consensus is to limit intense weight training sessions to 45-60 minutes. Some guys like only 30 minutes, some guys still go up to 2 hours. It depends on many factors such as nutrition, rest, intensity, frequency, etc. If training 3 times per week, 1.5 hours per session is probably ok. If training every day, keep it under 1 hour.
At this point, don't get bogged down with the details. So, don't worry about suppressing testosterone levels.
Regarding cardio, it sucks. There are better ways to lose fat. Note that I did not state easier, but better - higher intensity and lesser duration. There are ways to do this with weights or running or pushing cars and so on and so forth.
Finally, regarding what you heard many trainers say ... be careful. Just because someone gets paid to do a job, that doesn't mean they know what they are doing! Now, there are some VERY good professionals out there, but they are about as easy to find as an honest lawyer.