My blog is like 3 days new, some of my articles are indexed. I don't like the >> blog archieve >> I think it's going to effect my organic traffic from google...
Well, it will not impact you traffic. There is not big difference between using that sign, or - or |. All these just helping to end users. But it takes some space from your title. In you example if you will use "word1, word2, ..." it can add one more word to the title.
I'd rather suggest to use Platinum SEO plugin for Wordpress. It's same as All In One SEO but have some extra settings. After installing and activating it, you can change the Blog/Page/Posts Title and customize them. Additionally using the sitemap generator will help the old titles to be replaced by new titles quickly.