How Long Can UK visas be on deferred status?

Hi! My husband and I applied for visas at the same time by mail to New York. According to the websites visa applications generally take 5-10 working days. It's been 15 and our flight date is coming up very soon. I called the paid hotline service but all they could tell me is that my visa is on "deferred" status - they wouldn't say why or for how long. Does anyone know if this is usual and if I can do anything about it? I'm going to be a graduate student and my husband a teacher but at this point the year is starting soon and I don't know what to do.