When you receive your electronic permit to Mexico, you will see two dates on it. «Date of permission» — this is the day on which permission was granted. «Expiration date» always 30 days later than the date of issue of the permit. To summarize, the validity period of an electronic permit to Mexico is always 30 days.
But this is not the period during which we have the right to stay in Mexico! This is the period within which you must enter the country. In other words, the last day you are required to come to Mexico — this is the «expiration date».
Have you bought a tour or plane tickets to Mexico, and there is more than a month left before departure? Don't rush to make an electronic permit! You can compile it at any time before departure. Most importantly, don't forget to print it.
What to do if plans change and you don’t have time to arrive in Mexico before the “expiration date”? It's simple: make a new electronic permit, it is completely free of charge, and it is very easy to purchase it yourself. Instructions —Here
You can apply for new electronic permits as many times as you like. At least every day! You even have the opportunity to obtain a permit on the way to Mexico at the transit airport, if you have time to print it out.
At passport control when entering Mexico, you will be required to obtain a tourist migration card (FMM). The migration service officer will indicate the number of days you can stay in the country. Usually this is 180 days, but sometimes less.
These 180 days will begin from the day you enter Mexico, not from the day you purchase the electronic permit. Once the FMM is issued, the electronic permit will no longer be valid. You don't need it anymore, so you can throw it away.
Thus, it is at the moment of crossing the Mexican border that it will become known how long you have the right to stay in the country. The FMM card should never be lost — it is your guest sovereign visa; it proves that you are in Mexico legally. When you leave, it will be taken from you. Without an FMM card you will not be released from the country.
It does not matter what the validity period of the electronic permit to Mexico is. It is important how many days you will be allowed to stay in the country according to the mark on the FMM migration card.