The testing period depends on what the product is. Sometimes I just need to test an item once, and other times I need to test an item hundreds of times before I'm ready to write the review.
The actual writing of the review varies, too. I've written some of my reviews in 30 minutes or less. Then, I've had ones that have taken me hours. Lingerie reviews for me are usually very quick, as I've written so many at this point.