I know that when we used to move cows about 5 miles AFTER we put the bulls in we would notice a window of time where we would have a lull in calving.

But I think there is more to the story. Are the bulls trailed with the cows or brought up the next day? Are the bulls trailed or hauled?  What is the plane of nutrition (cows) at that time? Are you changing from lush feed to hilly pasture and the cows might go  downhill for a bit until they adjust to the change in feed? Are you on a good mineral program? We got on a good nutrition program and don't notice the 'lulls' happening anymore. Get over 85% bred in the first heat cycle.

Might be something to take a look at.