I had them pop me for one on the way back from Lima once, they came onto the jet bridge while we were deplaning. She wanted me to sign the form and start the clock ticking right there. I explained to her that I was not legally back in the country yet, and that even though we have priority in immigration, if there are other crews waiting or not many lines open, it can take quite a while to clear. I told her I would be happy to meet her on the other side of customs and sign the form there. She told me that would be a refusal to sign and she couldn't let me leave. It wasn't like I could go anywhere in between. Finally we settled on adding extra time to the alotted window, but man what a fiasco