First Class Mail is delivered in three to five days.
For Parcel Post, it would take up to 4 weeks, but from IL to PA, i would say 2-7 days.
Parcel Post is generally delivered within 2-9 days. Given the distance from Pittsburgh to California, it would likely take from 5-9 days.
Depends a lot on where you are and mostly where the other person is. I live in rural Alaska. It takes forever for stuff to get here. However to Anchorage, Fairbanks, Barrow. It will have less time....