it does that to let you have an idea how much traffic is on route. timing is not important tbh as you might want to leave early. you can check the widget to get a quick idea on how soon you can reach home and so on.
the widget however does use date and time estimates for other suggestions. for example... if you tend to visit a relative on weekends, if would show traffic situation on that route automatically on the days you usually go. if you check movie timings on a particular day, they would automatically appear in future on the same days.