I agree with LT. I think it can be about trust and I also think it can be about being experienced with knowing how therapy works and being transparent when you're in a therapy space with somebody who seems like a reasonable fit. You kind of get how it works now so it's easier to build a new relationship. That's definitely how I felt when I started seeing a second T for EMDR. I just rolled out the things that I needed her to know, and her reaction told me that that was a fine thing to do.
I don't think there is a timeline of what is right or wrong, but I do think it can be helpful to talk about it with your T. It's also not an all-or-nothing thing. You can check in with yourself and sort of lean in or out of the relationship based on how you are feeling.