Could you give me more details about that value placement? You've said that it should be behind the current time, but I'm not quite sure what do you mean. Should it be shown exactly behind the axis label? Illustration would be great here.
Of course such plot line can be added dynamically based on specified conditions. If you want something like that ten tell me when such line should appear or for which specific points.
Also feel free to ask any further questions.
Regards!