I usually insert Cidr's in the 45 day range . I always thought it was a great way to sync a group of cows and in my opinion nothing jump starts heats any better on beef cows suckling calves. About three years ago I had a group I was doing and a cow that had calved 30 days before was in it and I went ahead and cidred her, she had a good strong heat and AIed her and she went from having the last calf that year to the first calf the next. It works for me to insert Cidr on Wednesday with Gnrh, pull, lutalyse and Estrus Alert patch the following Wednesday with heats starting on Friday and rest of weekend.