Visitor visa question

[mohankul]

My parents are planning to visit US for about 6 months starting next April.

They will apply for visitor visa.
When would be the best time to apply for a visa? Do they usually grant visa only for the duration (say 6 months) or longer than that?

I want to know if they can take the interview in December and still get six months or longer visa from April.

Thanks,

Mohan

[immihelp]

Visa is valid from the day it is issued and the person can visit at any time before it expires.

The visa duration can't be predicted by anyone, but most visitors visas are given for at least 6 months.