Much depends on the state of your soil and the plants growing there now. Probably a lot of perennial weeds if it was allotments, so at least 6 months of light excluding mulch is required, probably more.
I think Back to Eden is a US film? If so the climate is diiferent to here and that affects things too, especially as they seem to have less slugs and can use thicker mulches of less decomposed organic matter.
What organic matter can you source cheaply and close to your land? How much of it do you want to grow on next year? – I suggest that less is more when you do it well. What do you plan to grow? All these things influence how to clean the soil, and how much of it you need.