Our research indicates that in North America, it takes thirty-nine days. In Europe and Asia, thirty-eight.
I'm kidding. It's impossible to answer this question for a variety of reasons, not the least of which is "Does a team ever really complete the process?" It's more of an ongoing process, like a marriage.
Another reason why it's tough to answer is that so many factors influence a team's progress. I'll list them here in the form of questions, like Jeopardy:
How much time has been set aside for team building?
How committed are the members to becoming a team?
How many members are there?
Are they all located in the same city or office?
How much history ...