How Long Does It Take to Adapt to Different Environments?

In a future where humanity is a space-bearing race or species, will there be humans that live on Mars? When they return to Earth, would they experience gravity differently while humans that visit the moon at the moment? Yes. With the going to Mars, we've got three possibilities. We can change our genetics to adapt ourselves to different environments but shifting from one environment to the other will be messy. No eyes, thanks for your answer.