<p>As far as I know resin trays have a Teflon coat that allows prints to stick to the build plate easier than the resin tray but this Teflon coat wears over time.  </p>

<p>I am new to the SLA scene and am currently troubleshooting a Draken Facture and trying to hone in my setting but my print keep sticking to the bottom of the resin vat.  </p>

<p>How often should these trays be swapped out to allow for smooth printing?</p>

I did some research and the life of the resin and resin tray appears to be dependent on how you use it.  For example, regarding the resin, 3dfacture states
"We see almost unlimited shelf life of the resin as long as it is kept out of light"
.
I know you asked about the tray and not the resin; but, the two are inter-coupled to the same fundamental issue.  Their lifespan is highly operational dependent.  If your printer operates in an environment that have very low ambient UV, the tray will have to be cleaned less because of less resin buildup and replacement and thus less wear.  Other factors come into play as well regarding cleaning procedures, usage amount, etc.
I think if you want a number you are going to have to run your own experiment in your own environment.