S.C.
It's easy for first time parents to feel intimidated by a care giver that seemingly knows more than you do about babies. However, you have every right to call and expect an answer within a one to two hour period, particularly when the provider has a cell phone and a land line available. Remember, she's not doing you a favor by watching your child, you're paying her for her services.
Let her know that you are concerned when you don't hear back from her in a timely manner and ask the provider when the best time of day to call is. If you're not comfortable with her response and are feeling increasingly concerned/anxious about your child's care during the day, consider switching providers.
Trust your instincts and don't blow off warning signs. Your child's safety and your peace of mind are of the utmost importance.
Best wishes.