If you have a proper warm spot in your snakes enclosure, then likely it is going about 3-5 days after you feed it. I have used the same type of substrate and it is easy to miss the leftovers. If you can look from the bottom, you might see it then, especially if it likes to borrow..... Look in the corners and bottom perimeter. If the snake is settled in at all, it may have started to go in one area. Just need to find it.
Another little trick with your snow - after handling it a few minutes and it calms down, hold it up towards a light bulb and look along its body. You'll see some of the ogans (heart, lungs, food if it ate recently) and the waste if it is close to going. If it is impacted, the location of the empaction will get firm, but not rigid...
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2.3 Albino Nelsoni Milksnakes
0.1 Snow Corn
0.2 Sunglow Corns
1.1 Albino Motley Corns
3.3 '04 Albino Corn hatchlings
1.0 '02 Albino Stripe Corn
0.0.12 Sunglow/Moltey eggs simmering
bunch.bunch Bearded Dragons
Bunch.unch Crested Geckos
0.1 Great wife
2.0 Great boys
0.2 dogs (they're great too!!)
and Corey's Yellow Knee Tarantula "Fang"