I'm not sure if your question is pre-supposing that you have to fill out the application EXACTLY three days before. The rule is NO MORE THAN 3 days before. If you can't fill it in on that date, you can do it the next day. Or as Mikel suggested, just start to fill in the form and put in a date which is three days or LESS from when you want to travel, in order to see the questions. And if you start to fill in the form, it does save some of the information, so it is somewhat helpful to fill it in early and then go back to the form when it's actually time to submit.

It really does not take that long to fill in the application, but I do agree that it would be helpful if they had a blank form online for folks to look at, to know what to fill in on the form. You WILL need your passport numbers and your flight numbers in order to fill it in. If you are vaccinated and boosted, you will need to have your vaccination results also, so make sure you know where you can find that copy of your vaccine records. When I had all that information in hand, I would say it took no more than 10 minutes to fill everything out, and I was being pretty careful to try to fill in everything correctly.

One thing that threw me the first time I did the form is that the dates are in the European format. So February 10, 2022 is 10-2-22, not 2-10-22.