We keep the shavings covered with paper towel for about a week. By then they realize what their food is and I don't have problems after that. I had a big hatch one time and tried to skip the paper towel step. A bunch of the babies were eating the shavings and choking on them. That's why I always give them a week on paper towel first, to learn what food is.
I used paper towels for 3 or 4 days before I put the pine shavings in. Our TSC put them on pine shavings from day one. When I saw them again at around day 7, many had pine shavings in their poop which was stuck to their butts.