I agree with the rest of the answers but to answer the what is the time difference question directly.
Roy Osherove in his book The Art of Unit Testing, Second Edition page 200 did a case study of implementing similarly sized projects with similar teams (skill wise) for two different clients where one team did testing while the other one did not.
His results were like so:
So in the end of a project you get both less time and fewer bugs. This of course depends on how big a project is.

