I don’t drive every day, so those who do may have differing opinions…
Morning rush hour usually starts to tighten up sometime after 6am, and is probably at its densest by 8. It’ll usually begin to lighten up by 9.
Evening rush hour can start as early as 3, and typically will be loosening up by 6.
Of course, road construction or accidents can change this, but weather is the biggest wild card. A thunderstorm or (heaven forbid) snow will make the commute a very long, very slow mess.
Weekends are, indeed, typically lighter, especially in the mornings. My favorite time to drive on the expressway is Sunday morning; it’s usually very empty. However, on Saturday evenings (and Friday evenings, as well), we often have pretty heavy traffic inbound, as people head into the city for entertainment. In addition, you can get very heavy traffic leaving the city on Friday evenings (and returning on Sunday evenings), particularly in the summer months, as people head to weekend destinations, often in Wisconsin, Indiana, or Michigan.
Also, if there’s a sporting event or other big event in the city, that will usually cause traffic tie-ups.
I’m not sure of the distinction you’re trying to make between “Interstate traffic” and “traffic within the city”. Do you mean surface streets in the latter? Nearly all of Chicago’s expressways are also Interstate highways (the primary notable exception is Lake Shore Drive). We have two separate sets of expressways / Interstates in the Chicago area:
- Those which head towards the downtown area (and which tend to be more strongly affected by rush-hour traffic)
- “Bypass” routes, which specifically go around the city itself. There are two primary “bypass” interestates: I-294 and I-355, both of which are tollways. While they don’t necessarily get as jammed up during rush hour, there are enough people who work in the suburbs, and use them for commuting, that they can get very busy at those times.
If you’re coming from Indiana, and heading towards Madison, your best bet may be to take I-80 to I-355, then I-355 to I-90. Or, if you want to avoid the Chicago area as much as possible, take 80 all the way west to 39, then 39 north from there.