It took about two hours to move the four old Blogger blogs over to the new Blogger, and this is my first 2,000 Days post with the new system.
I was pleased to find out, in my pre-move tests, that the new Blogger is just as good with old browsers as is the old Blogger. In fact, I started a new blog, This Old Browser, just to test this theory before making the move. Then it took Blogger a whole month or so to re-invite me over. I don't mind it taking two hours, but the first message I got indicated that it would take two minutes. I guess it gets more complicated when you have multiple blogs on both the new and old systems. But it happened, and everything looks great.
And publishing a blog post in the new Blogger is quicker than it was before. There's a benefit for you.