The best that I can tell you is that it will take at least one year, but will probably take much longer than that. Each patent application is unique. Different art units at the PTO have differing backlogs, so some take dramatically more time than others to even begin to examine the patent.
Additionally, you never know how many responses you will need to file. I have worked on patent applications that were issued in the first Office Action. I have also worked on applications where I was filing the ninth Office Action response.
Does the application automatically become a patent?
The PTO will examine the application and determine whether or not it should issue as a patent. Even if they reject it, however, you still have a chance to amend your claims or argue that the rejection was improper as explained on this article – https://pathofex.com/invention-journey-with-inventhelp-patent-services/.
When can I file a patent application?
The best practice is to file the application as soon as is practical. There are various reasons for this. For example, if someone else invents the same thing but files before you they enjoy a presumption that they should get the patent. Moreover, if you wait you may be prevented from enforcing your patent against others. Additionally, more art will continue to accumulate that can be used against you. Ultimately, waiting will almost never benefit you and waiting can be very detrimental.
You can file the patent application as soon as the invention is complete. You do not have to build it. However, you need to have enough information that you could build it. That is, the idea needs to be sufficiently complete that you can “practice” the invention.
Also, you can file the application up to one year after disclosing or selling the invention (in the United States, most foreign countries do not allow this one year “grace period”). Although the PTO rarely checks this requirement, it could be used even after a patent has issued to invalidate your patent.
There are mechanisms available to file quickly as described on https://www.companionlink.com/blog/2021/12/the-benefits-of-patent-services-from-inventhelp-experts/.