So I've been learning gdscript for a while and finally started actually practicing in the engine 3 days ago. And I've run into an issue with a for loop, except it may not be the loop itself that's the issue?

I'm trying to make it so that once this plant has been watered, every 5 seconds it'll grow into it's next stage. However once those 5 seconds are over, instead of going into the first stage it jumps straight into the final stage. And when I used print to keep track of the thing's values I saw it wasn't stopping...
(Also I just realized I wasn't printing my sprite's frames there, whoops.)
I can tell this isn't the loop's fault, because if it was then it'd be increasing every 5 seconds instead of every frame.
Does anyone know what I'm doing wrong here? Is += not what I thought it was? Am I just completely missing something?