which is it for crisssake?

[The Duck]

Doyle the rule of thumb on this is that on Tuesday and Wednesdays of even numbered months if the Tuesday or Wednesday is an odd number then number one is correct. If the month is an odd number then the reverse applies unless daylight savings time is in effect - this of course is complicated by the fact that the US and Mexico observe different dates for changing over - some unlucky travelers [called Tom Dooley's] are still stuck [for years it seems] at the border having been caught in this twilight zone.*

BTW the 2nd link you have is for an an arrival by air not land and that probably explains why you can only bring one cell phone - bring two more would subject you to excess baggage charges by the airline so its a helpful little 'gift ' from Mexican immigration limiting you to just one phone.

*Oh, I forgot to mention that the rules for the other days of the week are determined by three tosses of a coin between you, the Mexican immigration official and Jill Kelley if she is available by e-mail.