Having done voice tracking for years during my DJ years at a Salt Lake City FM, I can tell you that if you never hear the time or weather in a given hour, then most likely the shift is being voice tracked. Music is queued up in the computer to fill the hour, usually 12-14 tunes depending on the format. It is unusual for a voice track to go over the top of the music too, unless this has changed in the last 2 years. I would look at the screen and there would be four to five songs in a row, then just prior to a commercial load, the screen would say "Talk." I would hit the button and say whatever I had to say and then hit finish. My talk was usually back announcing songs or announcing an upcoming event or a short liner describing our format. There would be three "Talk" settings per hour (so I would use about 60-90 seconds in an hour). I would do a six hour Sunday shift in about 30 minutes on Friday night. I had some people fooled though, as I would actually give the time. My PD didn't like me doing that, but I did anyway. I could usually surmise the time within a minute or two of being accurate. I would go to Church on Sunday and people would say, hey, I just heard you on the radio a few minutes ago and you told me what time it was. I used to get a good laugh out of this until I explained to them about voice tracking. Any more, I truly believe most stations are using canned satellite feeds with central hub DJ's just playing hits and talking and they distribute that programming to 100-300 stations at once. I know Clear Channel uses something called Premiere Choice, that is what I just described. They'll have a live morning show on most stations and then to Premiere Choice based on the format they are using for that station. Just for laughs, I remember one week I said on Friday night that it would be sunny and 45 on Sunday and I woke up to snow (about three inches), and I rushed over to the station to change my voice track to match the reality of the weather outside.