For Call Centers, Business Processes, and other backroom activities then the time separation may be less of an issue. The assumption here is that these functions don’t require a whole lot of interaction between the people in the US and the people offshore.
However, if you are developing software products, this “benefit” does not apply. In this case “working around the clock” is as big a myth as “the mythical man-month.” Even trying to do testing at an offshore facility is problematic, particularly when the teams’ working hours have no overlap whatsoever. For example, having daily standup meetings with people who are more than a couple of time zones apart is not sustainable for most teams.
Engineers need to talk directly to one another, as often as possible. Product Owners need to be in direct, close contact with engineers and not through an offshore Engagement Manager or some other bottleneck. Everybody needs to talk to everybody all the time.
In the traditional offshore setting, the teams will play email ping-pong, sending questions and counter-questions back and forth. One team will ask a question today only to get a request for clarification to the question the next day. This is very frustrating to both teams and causes delays and quality problems.
On the other hand, working with folks in Mexico removes these negative side-effects. Everybody wakes up and goes to sleep at the same time and they can talk with each other and clarify any issues throughout the day.