What Cattledog is saying is on target. That being said, if you are going to syn the herd, you need to decide to close your eyes and work what works best for your schedule. You could breed for a week and then think that you are going to put in the cidrs, but then what about the cow that was going to come in on day 8 or 9? It would be endless. The only way that you could possibly avoid the scenario would be to heat detect for 3 weeks first and then would have an idea of which cows to breed the first seven days and put your cidrs in the rest. Kinda defeating your purpose of syning I would think. My opinion would be to work the season around your schedule and go for it.
We have cidred our cows the last 3 years and are thinking of going back to natural heats with the help of a penal blocked gomer bull. We think that all of the expense of the cidr protocol maybe offset by the extra cost of feed and time involved in breeding off natural heat cycles. We'll see how it shakes out. Good Luck, Brent