Harvest all at once or different times?

I am a little over 6 weeks flowering. This is my first grow and I didnt have the money to get the right nutes so the buds on top lof the plant look ok but theres not much to the buds on the lower plant. When the tops are ready, can I cut them and leave the rest to grow or should I just cut all at one time?

i would let them all mature, and u can get tiger bloom and big bloom for like 15 bucks a piece