  Approved travel authorizations are generally valid for two years or until the passport expires if the validity period of the passport does not exceed two years. So it is best to apply for an ESTA early before your trip to the US. Normally, what is recommended by the Department of Homeland Security (DHS) is to complete the ESTA Request before departure of at least 00 hours or more. It is good to know that the DHS considers unplanned travel in advance and processes requests for last-minute or emergency travel.  Approved travel authorizations are generally valid for two years or until the passport expires if the validity period of the passport does not exceed two years. So it is best to apply for an ESTA early before your trip to the US. Normally, what is recommended by the Department of Homeland Security (DHS) is to complete the ESTA Request before departure of at least 00 hours or more.  It is good to know that the DHS considers unplanned travel in advance and processes requests for last-minute or emergency travel.  