Momentary concentration, is called khanika samadhi.
and For the dry insight worker only khanika Samadhi is required. Khanki Samadhi- momentary concentration - can be either kusala or akusala. This khanika Samadhi - ekaggata cetasika- can be weak to strong. At the brief moments of vipassana nana it is strong because it is focusses so clearly, as the difference between mind door and sense door is revealed. And at the moment of penetrating Nibbana it is very strong indeed, and is even given the name 'jhana' because of its strength. it happens in a brief flash..
without khanika samadhi one couldnt read a book, or even a sentence, couldnt watch tv, or tie one laces.