i.e. in the 8th period (of the total 10), in the last period when the sun is still visible. The sun is going away / giving way.

The Y-shape is important. It means night, or perhaps period of darkness.

The 10 periods of the day ought to be followed by 10 periods of night. This is symmetrical and the sum then becomes 20, the sum of fingers and toes and a natural base for counting.

And, indeed, in Tahua we can identify and count to 10 glyphs of this general appearance (GD47):

The top of the sun in Aa1-30 shows the sign of GD47, a sign of the coming night. The Y-sign at the end of the shark's 'arm' also tells us about coming darkness.