Last month, I covered my allotment with black plasting sheeting to suppress weeds, how long before weeds/grass is gead I can start digging?
Personally, I only use plastic to keep down weeds during the growing season and cut cross slits to plant through. Instead, I remove the top 2 to 3 inches of soil and discard them (well chopped) in the compost. Then I add soil amendments such as a cheap fertilizer called Milorganite, Bone meal, Sugar, Epsom salt and cream of tartar (a form of Potassium).
It depends upon soil temperatures. In the summertime in northern California it takes me about 6-8 weeks if I want to break up sod and make sure the weeds really are dead. We have a cool, mild climate here so if it's hot where you are (above 68 degrees above ground) the black plastic will help to heat the soil and speed the process. In the winter time where I live, it can take months. If the ground is any kind of frozen where you are or there is frost or snow on the ground around where you live, plan on it taking a LONG time, post thaw and into spring.
