"At what time does he go home?"

Translation: Am faint o'r gloch mae e'n mynd adre?

[HBee10]

I don't get why this one is mae e'n. I thought it might be ydy e

[ibisc]

Questions about where, when, how, why, etc are always followed by mae - they are adverbial in nature.

[DesertGlass]

Why does this day o'r gloch instead of amser?

[mizinamo]

faint o'r gloch is "at what time" when expecting a clock time as an answer ("at three o'clock", etc., rather than "tomorrow" or "in four hours") -- literally something like "how many of the clock" (or "of the bell").