Is June 18 MCAT vs. July 9 MCAT a huge difference?

I'm currently scheduled to take the MCAT on June 18, but am considering postponing it to July 9 since it would allow me to do way more practice passages and practice MCAT tests, and iron out the subjects I'm weak in. I'm applying this cycle and want to make sure I have everything complete and submitted early, but I know the July 9 MCAT would set my application back by 3 weeks. Assuming I have everything complete by the time the score comes in, do you think taking the MCAT 3 weeks later would...

Is June 18 MCAT vs. July 9 MCAT a huge difference?