Download Speeds Drop Dramatically At Night Between Certain Hours To Unusable Performance

I have the Cox High Speed Internet Ultimate.  When downloading files, I normally average approx. 2.4 MBPS. Recently, approx. the last 4 days, around 8-9 PM PST every night, my download speeds come to a screeching halt to approx.  41 KBS - 240 KBS. This makes my internet almost unusable at nights. I work from home exclusively and I'm a Web Architect so I need reliable internet. I'm paying $100/mo. for Cox High Speed Internet Ultimate but I'm not getting what I'm paying for! I have talked to Cox Support and of course they want to reset the modem etc. but none of that works. I know a technician is not going to come out at 9 or 10 PM. I'm assuming this is due to Cox needing to split a node? So what do I do? I'm getting extremely close to canceling my internet from Cox since it is not  reliable. and I'm sure others around me will do the same.