What is the best amount of time to exercise and really see results?

What is the best amount of time to exercise and really see results?
For instance 15 minutes, 30 minutes, 1 or 2 hrs (each day or every other day) and taht involve full body and all bdoy parts worked to the max.

According to science or experienced fitness trainers what do y ou think is the best amount of time? And do you think you can achieve results by working at home and not at a gym per se (crowded people and where many people do nto even see they are working they go more to socialize, LOL!!!) I mean there are tons of videos from certified fitness trainers that tape videos for the people who do not go to the gym and possibly get the same results as in the gym, cause it is the trainer guiding you in her video as if she was in person. Even they do modified exercise if the person at home do not own gym equipment also and can do it also from home fromt he videos.
What is the best amount of time to exercise and really see results?
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