is it possible to get 1k arcade tokens with the pass in 8 days just by playing ?

Sure, why not? It'll take a lot of games, but you can do it. If you get every single fwotd bonus from here until the 29th, plus the 60 tokens from the remaining missions, you're looking at 400-600 tokens from just first win games alone. Get an additional 50 or so tokens (~5 games) a day beyond first win and you should get it by the end.

Ok so...

There's 60 tokens available from the missions.

8 days of First Win of the Day @ 18 tokens per day is 144 tokens.

So that leaves you with 796 tokens to obtain in ~8 days.

To hit this you would need to earn 100 tokens per day on top of your first win a day.

100 tokens is

• 8 Summoner's Rift wins + 1 ARAM win or loss or
• 12 ARAM wins and 1 ARAM loss.

If you want to hit your target, the grind is going to be a long and tedious one but I can tell you now as someone who owns the skin, the skin is absolutely gorgeous and worth the time.

If you can't grind for that long, you'll need to spend some money on bundles to at least get some tokens to soften your grind.