My ping to huntress always takes a dive between 5pm and 10pm (aka peak network traffic time).
Neither the business nor residential networks peak during that time. Business peaks from 10am-4pm and residential peaks from 11pm-4am. At least in the US, anyway.
If you're suggesting that you're losing line quality or throughput during a certain time that *IS* something your ISP is obligated to fix. You are given an allocation of bandwidth and if they aren't fulfilling that you should be complaining. For a cable company, fixing this takes less than an hour rebalancing the local line, for DSL it takes the better part of a day but is actually more critical as it indicates an oversubscribed or 'about to fail' circuit.
Good luck trying to convince your ISP to give your IP more priority than your neighbor without paying for "business class" or whatever other name your ISP calls the top-tier service.
Residential connections are considered "best effort" but that doesn't mean "no effort." If your connection is fluctuating on a daily basis that is a problem on their end. Again, you should call and complain *EVERY* time it happens until they fix the problem. As Taemien said, you have annoy these guys and piss them off if you want things to change. The network admins in your area have thousands of households they're responsible for and don't have the time, resources, or sanity to diagnose and fix every little connection irregularity so they aren't going to even try unless you call and complain.