I think it could take weeks to kill it out. Grass can go dormant and then when it gets water and light again it magically comes back to life, that is my experience anyway. All the beds I did from scratch like that, I used round up on it initially to kill the grass. Then after a few days you can plant in it and be sure to mulch it heavily or new grass/seeds will come up everywhere. You may keep cardboard down on the path areas between rows to keep the weeds out there. I mulched my past beds with straw. A large bed like that is way to big to strip sod off. I have never stripped the sod even on small beds. You lose alot of nice top soil that way. Of course if you have a compost going, you can keep that soil replenished as you go. Do not buy your roundup in a ready to spray bottle, buy it in a concentrate and mix it-it's much cheaper that way. Then in the future once you get the bed going, if you have a tough weed, like bindweed, or poison ivy ect sprout up in there, you can just apply the round up directly on that weed to get rid of it. Round up is nothing you want to use regularly in your vegetables.
