The worst time is right before the sun goes down, on that time that is just INTO your eyes, no matter if you are in a car or riding a motorcycle, you cannot see anything.
In my city this is particularly bad because there's a long stretch of road that goes east-west and it's the main access to anything here, with the sun right on the spot that won't allow you to see anything in the afternoon. That and kids leaving school, the huge amount of parents parking their car wherever to pick up their kids, the school buses jamming up traffic and everything.
Another bad time here is when certain class of people need to go work, they move in motorcycles and they go in packs of 10~40. They're absolute danger because they don't respect any traffic law. They run red lights, they don't indicate turns and go around swerving without any warning. I'd rather ride trough a bunch of cars instead of between these people. I started going to work early to not meet them. They're on the street at about 07.45.
The best time is really early in the morning or past midnight. I like riding in the night because I get a visual cue when there are cars approaching, their headlights. It is a problem though because some stupid motorcyclists ride with no lights at all.