My husband was operated on for squamous cancer of the maxillary sinus. how long would it probably have been present to have invaded bone and muscle?

Hard to tell: Each cancer will grow at its own rate. No one can tell you how long he has had it with any degree of accuracy.

Depends: Although cancers can "appear" very quickly, they may have been present for years to decades before the diagnosis. Anatomical sites that are not easily seen (i.e. Sinuses) can harbor small, slow growing cancers for many years before they present with symptoms.

Transformation: In addition to the other answer, schneiderian papilloma are a certain type of benign tumor (many of which are in the maxillary sinus), that can undergone malignant transformation also -- but this is usually after years of having papillomas.