It's not so black and white!
There is no exact timeframe in a your career or set requirements you need to meet before you can register with a publisher like Songtrust or start your own Publishing Company. However, there are a few things we recommend keeping in mind when deciding if it is the right time for you to get setup with a publisher and/or create your own publishing entity.
The first thing to consider is if you plan on or have already released your original compositions for public consumption on services like Spotify, iTunes, Tidal, etc. Anytime your music is played on these services, you have the potential to not only earn money on behalf of the recording but also on behalf of the underlying composition (these are known as mechanical royalties)! If your songs are generating a lot of traction on these services, you definitely will want to get setup with a publisher like Songtrust, as mechanical royalties generated in the USA do not go through your local PRO, so to collect those royalties you have to have a publisher, like Songtrust, collect them on your behalf so that they then can be allocated back to you. Getting setup with a publisher at this point will help make sure you are collecting all of your hard earned royalties, and not just what is being generated on behalf of the sound recording.
The second thing is to consider is if you are performing any of your works publicly. Anytime you perform your works publicly, you earn performance royalties, and if you own your copyright, you are entitled to both a writer's share of earnings (which is paid to you by your PRO directly) and also the publisher's share (which is paid to a company like Songtrust or to your own Publishing entity, who then must allocate it back to the writers). However, it is also important to consider where you are performing - if you are only performing your works domestically, then registering with your local PRO might be enough. For example, BMI will pay you both your writers and publisher share of performance royalties even if you don't have your own publishing entity set up!
Another thing to consider is exactly where your songs are being played. If your songs are being played outside of your home territories, you definitely will want to work with a publisher that has direct affiliations with those territories so you can also collect those royalties as well. Your local PRO won't be able to help you collect royalties generated outside of your home territory.
The last thing to consider, is, even though you may have met some or all of the 3 criteria's above, how much money do you think your songs will actually generate? Starting your own publishing company or registering for a service like Songtrust, isn't free, so its important to think about whether or not you will recoup your original investment into such services.
Lastly, its important to note that having your own publishing entity is not the same as having a publisher, like Songtrust. If you create your own Publishing Entity through your local PRO, your publishing entity will only receive your share of publishing royalties generated from public performances and broadcasts within your local territory. Your own publishing entity cannot collect mechanical royalties for you nor can they collect performance royalties generated outside of your home territory. Currently the easiest way to get those royalties is to sign up with a publisher, like Songtrust!