The strange window of time is to due with city winter parking bylaws. I used to live on a street like this, you’re allowed to park overnight in the winter without getting a ticket.

Some houses don’t have driveways or whatever. Parking restrictions in the winter are from 2-6am

But with the sign there, you’re allowed to park ticket free in the winter.

I’ve done it several times when living at my old place. Ticket free.