They poop when the need to poop. There's no "schedule".
They will often hold poop with a shed upcoming. So if you're expecting a shed, expect a poop with it.
If your snake goes weeks and multiple feedings (of appropriately sized prey) without pooping, you may notice the build-up towards the tail, often referred to as "sausage butt". Until you see that, don't worry at all. If you see that, still don't worry, we'll help you out.