What people need to understand is that one "White Widow" is not the same as another. The "original" white widow is a hybrid of Brazilian and Indian descent. I am currently growing Nirvana's WW, and the site says 8-10 weeks. If time is the issue, but money/craftiness isn't, I would suggest a hydro system, as these can produce a flowering plant in 3/4 the time it would take with soil.
You also generally need at least 2-3 weeks of vegetative growth if you want a harvest that's worth anything