Aker means not only the moment, but also the place and situation, the situation of death and resurrection, of yesterday and tomorrow, of the resurrection and regeneration of the sun god.
Von Franz identifies Aker as the pivotal Egyptian underworld symbol — simultaneously temporal threshold and spatial locus — marking the enantiodromia of death into rebirth, which she reads as the alchemical and psychological ‘night sea journey.’
, Alchemy: An Introduction to the Symbolism and the Psychology, 1980thesis