How to interpret 休息不了多长时间吧？ 他是‘业余作家‘。

您在白天应酬、工作之后，晚上是怎样进入写作状态的，您晚上休息不了多长时间吧？

Have  I got this right, seems she is asking the question in reverse.

您晚上休息不了多长时间吧？ = How long do you sleep at night?

His answer is '我大概一天睡四到五个小时。‘ but her question says 'how long can't(不了） you rest'.
您晚上休息不了多长时间吧 is between interrogative and rhetorical. It means 


  (I reckon that) you don't have much time for sleep at night, do you?


There is a strong suggestion for the answer, yet an answer is expected to complete the dialog.

Word by word translation is like 


  You are unable to rest for long time at night right?