past simple tense

What does it imply - when we talk about an action that happened in the past using the past simple tense with a time expression like in the sentence "I washed the windows at 6 o'clock yesterday",
A) I started to wash windows at 6
B) At 6 I was in the middle of washing
C) I finished washing at 6

All your sentences meat that standard.

Hello there)
I'll be happy if you help me out with the following question.
What does it imply - when we talk about an action that happened in the past using the past simple tense with a time expression like in the sentence "I washed the windows at 6 o'clock yesterday",
A) I started to wash windows at 6
B) At 6 I was in the middle of washing
C) I finished washing at 6

A careful native speaker would only use the simple past, with a specific time, about an action that was either instant or complete at the time mentioned.

Since washing (or "cleaning" as we say in Britain) windows cannot be done instantly, if a native speaker said "I washed the windows at six o'clock" to someone, then that listener would probably want to ask the same questions that you have.

If that was anything but a silly repetition stolen from some other silly grammar wag, one might think to give it some consideration.

Hell, there is virtually no one, [native speakers], who asks questions about much more important things, for example, areas of the English language that confuse them badly, you included.

A careful native speaker