"Time till release is less than 3 days" So it's 2 days, if you count down till day 0.
59 Hours 53 min left until the Europe release (UTC+1, European Central time)
15th = 2 days EU, 1 day US
16th = 1 day EU, 0 days US
17th = 0 days EU, release US
18th = release EU
days are rounded down from 23:59,
That's why they're at 1 on countdown since they follow the US release day.
Not really how I would countdown either though, I would just keep day 0 as the day it releases, makes more sense to me, or maybe they were afraid that no one would post pictures with cars with zeroes if everyone went to play GT Sport.. but I find that a bit unrealistic as well, surely someone would be excited to post day 0 pics before they went to the store to grab their copy or before they receive it in the mail later that day.