[Lennert Schrader]

I found the solution!!!
I found it in this forum – sorry for not looking well enough before!

If anyone comes by, below is the expression I ended up using.

I added the last line of code, to change the initial starting number of my text layer (2853).
The number will begin to change from the second layer marker on.

Thanks to Walter Soyka – I used his expression from here:
https://forums.creativecow.net/thread/2/989308

m = thisLayer.marker;
i = m.nearestKey(time).index;

if (m.nearestKey(time).time > time){ i--;}
if (i < 1) { i = 1};
i--;

text.sourceText = i+2853