Offical Time Frame
The U.S. Patent and Trademark Office reports that on average a patent takes 22 months to receive approval. That's almost two years, and it may seem like a long time, but that's only an average. It also does not take into account any pre-application process or other common delays, so 22 months could be a fast patent.
Real Time Frame
The application process has no preset waiting periods. Each patent is reviewed on its own merits by different groups of specialists. According to the Iowa State University Research Foundation, the time between the application and the patent being issued can vary drastically and take two or more years.
The pre-application process can take a few months; then the application-review process, which checks if the patent is feasible, takes 12 months minimum and often much longer. Once that happens, the patent office sends a response, almost always asking for more information. This can take months, since the patent seeker is given up to three months to respond. If all goes well, you will receive a notice of allowance in three to six months asking for payment, or you will receive a notice of final rejection. After three or so months after they receive payment, the patent should be issued.
If you don't hear from them within five months, contact the patent office directly.