^I dun think the index will go back to 10K on weekend since there is no threat at all this time. Last time avex had to promote FREAKING HARD for the last two days to save the no. 1 spot from SCS. This time, well no one's gonna make them panic, so I dun think there'll be any special promotion during the weekend.
Also, like njanjayrp said, MW had an extra day, so if Days/GREEN has 120K on the first week, it's good to me.
Edit: it's almost 5000, not just 4000. If you have been following oricon sales, you should notice that Friday sales is always the weakest of the week. I expect it would drop below 4000, but actually it managed to sell almost 5K. That is considered GREAT.