It will be difficult to kill all the vegetation, then keep the soil bare till you are ready to plant new seeds. My suggestion is to strip the grass and weeds off the ground when you are ready to plant new seeds. When ground is left bare, it receives wild seeds of numerous kinds in the wind, rain run-off, and even bird poop. Wait and do your grass and weed stripping when you are ready to replant. After stripping the ground, I would till it, then replant.
