That depends on the lender and the workload the lender has. The first thing the lender will do is obtain your credit history. Next the lender has a professional appraiser view the property you intend to purchase. Appraisers can be very busy when the real estate market is up.
The appraiser files a report with the lender, which lets the lender decide if the property is worth the amount of the mortgage loan you are requesting. Finally, after all the documents are obtained, the lender reviews them in order to make a decision. The entire process will probably take anywhere from two to eight weeks, depending on the market, the time of year, the area of the country, and the appraiser.