Personally i use cstart a lot for playing in camel duels.
İ never had a problem with 5 second countdown but if it were 3 seconds it wouldnt be respected by people who play duels because it would cause them to lack preparedness.
İf it were 10 seconds, İ would consider that official for a clanwar, but İ cant afford to spend that much time waiting, if İm just looking for a not serious match.

İn the past it was customary to get ready before the countdown started. So that way, you can apply your own timing to the start of the game, without requiring more keystrokes to alter the countdown timer. İts just easier to do it mentally than manually for counting time.