Set delay buggy

I would like to add a problem I am having with attack delay. The increments of time are too large to be able to get the sepperate armies to hit exactly at the same time. this is crucial for being able to use air and support troops to hit exactly at the same time to reduce losses to certain units the closest I have been able to get multiple sepperate units to hit is about 4 minutes appart. I would like that number to be zero .. why cant we be able to set delays so hits are at exact same time.