when will i be able to tell if it is a male?????

So i have 3 clones right now and 1 plant i started from a seed (which I dont know if it is a male or female yet). My question is when will i be able to tell if its male or female? I know about the pollen sacks and all that but i have been told that i dont have to worry about it until i change the light cycle to 12/12. Is that true? Because right now im vegging and want to know if i should be keeping my eye on it now or not.

uv really got to wait until about 2 weeks into flowering b4 u will find out for certain but u really dont need to worry, it will show sex long before its able to polinate and give u plenty of time to dispose of it.