Your usage is throttled by time of day standards (4-9pm your time). If this is when the problems are occurring then the solution = upgrade your service package as they don't throttle higher package purchasers.
In the mean time, call tech support .. could be a simple modem or router issue. If it's not, file a complaint with customer service (politely) and if the problem persists ask for a discount (good will credit toward your bill, say 15% off for the inconvenience) for every month the issue occurs. They'll most likely do it. If it continues for more than 3 months, call back and ask to have your package upgraded to the next level at the same price you're paying now - they'll most likely do that, too. Customer service & tech support will deny that you're bandwidth is being throttled by time of day standards, but they WILL compensate you for the problem if you complain enough in a polite and straightforward way.
Source: 1) Experience (I get tons of free stuffs & discounts from Rogers), and 2) confirmed by best friend who works for them.