Internet Speed during prime time

This Friday night and Saturday night during prime time hours (6pm to 10pm) I have had virtually every movie and video I was streaming buffering, giving me warning that my service lack sufficient speed to continue, even stopping and recommending that I try later. I have a preferred account and should have a download speed of 25. During the week I have not problem getting this kind of download speed as proven by speed tests that often run up to 30. During prime time hours I have been getting download speeds from 2.9 down to 0.22. When using the Cox preferred speed test, I couldn't even get a reading. With all the talk about faster speeds, can anything be done about slow speeds that interfere with streaming movies and video? p/s I have had no recent changes to my internet service.