Dear Visa Now:
We must first note that we are not immigration lawyers. While we can comment on your friend's situation from personal knowledge and experience, we clearly lack the detailed and precise knowledge of the immigration laws and process of the US government.
The H4 visa in the US is granted to the spouse and dependent children of an H1 visa holder. Anyone applying for the H4 visa must produce legal and official documents to prove the relationship and dependency on the H1 visa holder. Since your friend has not married yet, his prospective wife has no legal or official relationship with him. Thus, she is not qualified for the H4 visa yet.
An H4 visa holder can stay in the US legally for as long as the H4 visa is valid and the H1 visa holder, on whom this person is a dependent, maintains a legal valid status for the H1 visa. It is not uncommon that the H4 visa is of shorter duration than the H1 visa; however, the H4 visa can be renewed provided all requirements are met.
The time taken for the issuance of an H4 visa depends on too many variables, not the least of which is the individual situation of the applicant and the sponsor. This time can vary widely.
Dear Mentor:
