|It's common practice to arrive late to weddings in Mexico|
Mexicans, due to many cultural and historical reasons, in general have a less concrete concept of time. This reflects in a much more lax abiding to schedules and planning. If you aren't familiar with this concept, what you'll notice is that Mexicans tend to arrive late.
However, the management of time in Mexico is much more complex than this symplistic "Mexicans are late" stereotype.
For example, if you are an employee for a company, you will be expected to arrive on time. Some companies will tolerate 5 or 10 minutes or even half an hour, but only on special occasions. You certainly can't arrive late every day or with frequency without consequences.
Also, in some situations, it's ok for a person to arrive late, but not for the other. One clear case is when two people from different hierarchies arrange to meet. The boss may arrive late without any need to give an explanation, but the employee may not. This system also works when one person needs something from another person meet. If a person needs a favor or something else from another one, he or she will have to be on time while the other person may arrive late. This attitude is very common when you're meeting a client or when you go to the doctor. In addition, when making arrangements for a date far in the future, it's always better to call the day before and ask if the plan is still on (Mexicans call this practice "to confirm" as in "I just called to confirm that the plan is still on.)
Social reunions are a different matter. Since Mexicans think of free time as "not work" they believe that there is absolutely no reason to subject themselves to schedules, like they do with work. Thus it is common for people to arrive at parties with 30 minutes, one hour, or even two hours later than the announced hour without anyone considering it rude. In fact, the host will often say something like "I'm glad you managed to make it, I was afraid you weren't going to come."On one on one interactions, for example, f you are meeting with a friend for the first time, expect him or her to arrive up to 30 minutes late.
What are the benefits? A much more relaxed way of life. You'll find that Mexicans don't behave as rushed as Americans (again, there are tons of exceptions), and they take their time to "stop and smell the roses." It also allows for more flexibility, for example, you can always stop on the way to a party and buy the present that you forgot to buy the day before. I personally carry a book with me all the time and try to agree the other person to meet at a place where I can sit and have a cup of coffee.
Finally, as with every culture, people tend to react to your actions. A person that always arrives late (or worse, doesn't show up at all) with no call, with no explanation, with no apology, will soon run out of friends and clients. Time in Mexico is not a carte blanche either.