I live in an apartment building, each unit has a separate electric meter. I have noticed that the incandescent bulbs in the bathroom flicker quite visibly in the morning, but not usually at other times. I am not running anything else except for clocks or possibly the fridge (which cycles itself on and off) or the water heater (ditto). It is winter, so no A/C is running, and we have electric heat (not heat pump).
Why would the lights flicker only at certain times of day? I figure that I only notice it in the bathroom due to it being a small brightly lit room with no windows, not sure if light bulbs flicker elsewhere in the apartment at those times. I sometimes observe a single flicker occasionally in other rooms at night. This did not happen when I lived in houses.