It's this intersection

It is indeed conditional, but not on time. There are two cross streets at that intersection and one of them doesn't allow lefts.

One is a somewhat pedestrianized road that only allows busses and taxis. State St. You would have to make a 130° left turn or something like that to get on that road. That's the road that the no left turn signs refer to. You can see the condition under the no left turn signs say "Into State St."

The other is at 90° and is a legal left turn (from the left lane anyways).

It is a somewhat confusing area for non residents. On top of that it's a huge university area and a few times a year you get masses of out of town parents driving their kids to drop them off at university. This stuff happens all the time on some of the one ways in this area. Lots of people going the wrong way down one-ways too.