When do i cut the top off my plant?

My plant is 8 inches tall and is 3 weeks old i want it to bush out but i dont know if i should cut the top yet please respond.

Sry im a noob but its my first grow.

no dont cut the top........just pinch the top node ,....take finger and thumb and squeeze it til you feel it give then watch for 4 days the bottom branches will grow out and come to the top of the plant after that you can pinch every node even the branches allowing time between,...like 4 days this will make it amazingly bushy, ive never topped just use this type of low stress .BY doing this it make the lower part of the stem very big around and hardy like a stick not like that little feeble weed you have now and when you go into flower this allows the plant to hold more weight...........you did want more weight right?