What is the maximum time allowed to land in US after H1 visa approved date


I have done with my visa interview for H1B on Feb-12-2016 and went through successfully.

I am planning to move to the US in the second week of May 2016.

Is there any rule like after these many days of your visa approval you have to be in the US.I heard its like 90 days.

Does such rule exist? If so what is the maximum time frame?

There is no such requirement. You can enter US anytime during petition and visa stamp validity period. Whenever you enter US, ensure you have recently dated documents like employment letter, client letter etc. and that your employer supports your move to US along w/ employment here.