During one of my first grows, I had similar time restraints where I could only get into my growroom at varying times during the day. I remember taking a fairly thick piece (3-4cm thick) of green plastic, and basically just taped it to the lens of my flashlight when I needed to see in the dark. Only a dull green glow was emitted, just enough to illuminate what was right in front of me. I even had to do this several times during flowering, and never made a plant hermie from it. But, if I knew then what I know now, I would have tried my damnedest not to do it at all. If you absolutely have to, I think there may be some truth to using a dim green light...but I unfortunately don't know how much water that theory carries.