Visitors are advised to submit their TWAC at least three days before coming to Taiwan, but can also do it at the airport, where free wi-fi is available.
For families or tour groups, one person may fill out the form on behalf of up to 16 individuals.
Yeah nah. We don’t do that.
I believe that’s incorrect in the article, I think it should be at most 3 days before arrival, i.e. you need to wait until near flight day before you can apply.
Malaysia have had a similar system for nearly a year now, it a bit of a PITA when on trips to multiple locations as you can’t apply before setting off, need to wait to at most 3 days before arrival. If you have your own internet access it still beats filling out slips of paper I suppose as it’s a lot of private information to be sharing over a free wifi network in an airport.
Not travelers, but visitors.
Major issue about the Taiwan Arrival Card:
It only lets you fill out the arrival card three days before arrival based on the local system time 
I wanted to help my parents fill out theirs - called them after midnight (Taiwan time) - and the website in Germany only shows yesterday, tomorrow and today.
I had to guide them to change the time zone of their computer to Taipei before being able to continue…
What happens when your flight number and arrival time (same day) are changed one day before the flight? But online form was already completed. Should you /can you modify or make a new one?
You should be able to update it online using this:
As long as you submit the correct info before clearing immigration it’s ok
Thanks @Mataiou and @cranky-laowai