How can some players time their attacks so perfectly?
Every game world has a duration offset of 10 seconds, which adds a random time element to the attack, making it difficult to time attacks in an exact manner.
However, it is possible to cancel and resend attacks, to get closer to the desired results, and there are several different ways to do this. Many veteran players are experienced in timing attacks. Your best bet is to ask your alliance how to achieve the best results.