If you're affiliating with a Performance Rights Organization (ASCAP, BMI, SESAC) for the first time, the earliest you will see royalties is 9 - 12 months after affiliation.
Note: this lag time is standard for all Performance Rights Organizations, whereby there is a minimum of 6 months between the use of your songs and royalty payments.
If you are already affiliated with a PRO at the time of joining Songtrust, you should not see any interruption to their performance royalty collection. It typically takes about a year after joining Songtrust to see royalties from additional sources like mechanical royalties and international performance royalties.
If your songs aren't being meaningfully used (sold, streamed, broadcast on TV, played on radio, etc.), no royalties should be expected. Joining Songtrust in no way guarantees that you will be collecting royalties.