use a different ISP!!!
My VM connection is usually dreadful between those times too and I hardly ever download anything. If I do, it's just a game patch or my email, so capping is not the answer to my issues. During the day, I get full speed and gone about 11pm I get full speed, but in between the times you mention, I regularly get under 3Mb. I have seen it on a number of occasions as slow as 300kbps.