[Observium] Drilling down to specific times in graphs

I'm having a little trouble understanding how the graph drill downs are supposed to work.

I select a 6 hour graph of something, From: says 17:44 To: says 23:44.

Case 1:

I change 17:44 to 16:44 and click Submit, From: says 11:44 To: says 18:44.

Case 2:

I leave From: at 17:44 but change To: to 18:44 and click Submit, From: says 12:44 To: says 13:44.

Am I missing something on how these timeframes are supposed to work?