Exactly what I did last night!!!! You weren't sat next to me were you???
I believe the following FAA regulation answers the question from their standpoint.
Part 135.207 VFR: Helicopter surface reference requirements.
No person may operate a helicopter under VFR unless that person has visual surface reference or, at night, visual surface light reference, sufficient to safely control the helicopter.
If you haven't got 'visual surface light reference', which at night offshore you haven't, then you become IFR.
I will admit that I don't operate under their regulations so I could have found the wrong one.
Here we depart Night VFR, travel out IMC and land with a combination of VFR and IMC.
