IMDb is not the most reliable source for episode information. On the Prime page (the original network for this series), it says October 4, 2018 for season 3.

As for The Grand Tour, of course the dates on Prime indicate October 4 but I find trailers that speak of October 5 https://www.youtube.com/watch?v=jB6AWesDNLU or promotional tweets https://twitter.com/HighCastleTV/status/1020846852973899777 https://twitter.com/HighCastleTV/status/1047174170335801344

On the Prime page (the original network for this series), it says October 4, 2018 for season 3.

Prime Video Originals come out on the advertised day at 12am GMT, making the US release date the day before at 7pm ET. I've checked a few Prime Video Originals on the site and some only use the advertised date (like The Expanse Seasons 4 and 5), some only use the US release date (like Carnival Row), and some use a mix of both (this show uses US release date for S3 while S1, S2, and S4 use advertised date; The Boys S1 uses US release date while S2 uses advertised date; Red Oaks uses advertised date for S1 and S2 while S3 uses US release date).