Ideas:

1. The idea of hiding, which seems to be the foundation of meaning in this type of glyph, is not the same idea as being in the dark. Being in the dark might mean to be in the shadow, and then perhaps the appropriate glyph is a shark, mango. E.g. when the dark part of the moon is visible in spite of being unlit by the sun.

2. If hidden means not visible at all, then I suppose that means not visible at any time during the night. But the Polynesians used to look for Matariki, the constellation of Pleiades, either in the morning or in the evening. If this constellations was visible, then the constellation was called Matariki i nika otherwise Matariki i raro.

When the Pleiades stars were visible in the early morning just before the sun goes up, that must mean that they keep that order all through the day and night, i.e. when the sun goes down the Pleiades have already gone down and that means that you cannot observe them in the evening. Therefore the time of the year must be Matariki i raro, the Pleiades below, a time when they cannot be observed in the evening (but only in the morning). But it seems that on some islands they watched for the Pleiades in the early morning, which means that for those islands this time of the year was Matariki i nika, the Pleiades above.

3. So I arrive at the conclusion that the 'hidden'-glyph is (at least in the calendar of the week) a technical term for being invisible because the 'planet' is between earth and the sun, its face turned away. This, then, is a different event than when we can see only part of the 'planet', e.g. when the moon is waxing or waning, or when the object is invisible because it is on the other side of the sun.