Snakes don't defecate regularly- on schedule the way dogs & other pets do- so I wouldn't wait- I'm pretty sure they can get a sample anyway (as they do for dogs etc. if you don't bring a sample).
You can mention this though. And for sure, take the material with the pink stain to show them- that's an odd color for blood. Have you tried to get that color (by rubbing with damp paper towel) from other items in enclosure? I sure would- & I hope you find this didn't come from the snake at all.