Ok, lets attack in one week.
From Create Your Own Story
So, in one week, the army of Gondor is rounded up and prepared for an assult on Mordor. After about a day of marching, the Black Gate is in sight.
Does Boromir:
Tell the men to unload the catapults and fire at the gate. Tell the men to get up close and wait for the gate to open. Chicken out and go back to Gondor.