Ive had to do this twice since the last post. A few comments in case anyone needs it...
Time wise it can be tight, very tight. AA crew doesnt leave the plane, so they have no issues. Staff there insisted I could not stay on board, that I needed to enter MX and go through immigration and customs
First time I was in F down and back, and only had carry on- which fit in the overhead bin on an MD80. I didnt quite grasp the drill, so I got off the plane, went through immigration and out through customs- then back into security, back to the gate. They were boarding.
I did realize that I could have just made a U turn and head back to the gates and not go through customs. Passengers streams mix at this point in the underground tunnel- there are some shops along there, etc. Just stop, look, then walk the other way back towards security. I noted this for future reference.
Last time it was a smaller plane, a CRJ9. I was in F but was forced to cabin check due to a smaller plane. Then, apparently in MTY they dont give you your valet/cabin checked baggage until customs (!!!! FML) Immigration was very backed up, this took 20 minutes. I had to race to customs, get my gate checked back, then back into security. I couldnt do the U turn trick. Lucky for me, security was pretty quick, only 2 people ahead of me. Flight was well boarded when I got back.
In MX, you will retain a part of the form in your passport which you fill out when you enter the country...then the gate agent collects that small immigration card. If you have not 'entered' the country (by not going through immigration) then when you try to reboard the plane you will not have that card. You risk being turned away. I also do not know if they match manifests and head count with mexican authorities. The link here is immigration, but not customs
Anyway, in the exceedingly rare event someone needs to flip in MTY!