I don't know if all Post Offices have them up yet, but when I scan a barcode on my route, it is uploaded into the tracking system within a minute. I have not checked to see how soon somebody's parcel's progress is visible online.
Today I saw that a parcel I had looked up in the morning, (it was exactly like the one I had needed a signature for yesterday, and I wondered if I had forgotten to write the attempt date on it,) showed today's correct scan when I refreshed the search on my cell phone when I returned from delivering.
Killdeer