When planning a trip to the US, or any trip involving a connection through an American airport, we strongly advice that you obtain your ESTA authorization well in advance. That being said, the validity of your ESTA begins as soon as it is issued, not when you enter the US. Here are everything you should keep in mind when deciding when to submit your ESTA application:
You need your ESTA to be approved already at check-in
Remember that you need your ESTA authorization already prior to your arrival in the US. For example, you may require a valid ESTA in order to be able to check in on your flight bound for the United States. Similarly, the airport personnel may check your ESTA status when boarding your flight. Thus it is important that you apply well in advance, so that you are sure that your ESTA will be authorized before check-in for your flight opens up.
The validity begins immediately upon issuance
However, one should also take into consideration that an ESTA comes into effect the moment it is issued. That means that even if you are months away from your trip, the validity of your ESTA starts immediately when it is approved. An ESTA will typically have 2 years of validity, and it can be used for several trips during that period. Thus, you may want to apply closer to departure to avoid wasting months of validity, in case you plan on returning to or transiting through the US subsequently.
Your application may be delayed
Another complicating factor is the fact that your application may take longer than expected. While most application are approved within a matter of hours, some applications may not receive a response for up to 72 hours. And at this point, additional information may be required in order to complete your application. To avoid being negatively impacted by a situation like this, it is ideal to apply at least a couple of weeks in advance.
In case of a rejection, obtaining a visa may take a while
If you are one of several groups of travelers whose application face a substantial risk of rejection, e.g. those who have previously traveled to certain high-risk countries in the Middle East and Africa, those with a criminal history or those who previously overstayed a visa. In such a situation, we recommend applying months in advance, so that you have time for applying for a visa through an embassy if necessary.
The best time to apply depends on your personal circumstances
If you are someone who have no reason to believe your application could be delayed and rejected, and if you are frequent traveler who may make use of your ESTA in the future, we recommend that you apply a couple of weeks prior to check-in. On the other hand, if you are someone whose application may face difficulties, we strongly advice you to apply months in advance. Similarly, for those who do not expect to make use of their ESTA in the future, we also recommend that they apply well in advance just for the added certainty.