Zoning and City Paper Work

I would like to buy a new home with room for my office on the same property but the zoning rules are telling me that I can't do that unless I go through a rezoning process. The City of Tucson zoning expert told me that the zoning change may take up to 3 years.

If I tell the seller that I would like to get the zoning change approved first, they will probably sell the property before I get a response from the property owner.

This is frustrating and unreasonable.