I get up before 8 am, wash my face and brush my teeth, and then have breakfast.

There is nothing wrong with what you wrote, but stylistically it sounds a little odd to end one sentence with "I don't get up early" and then begin the next with "I get up before 8 am", because the concepts of "not early" and "before" are kind of inconsistent. It would sound less odd if the second one began with "I get up around 7:45" or "I get up after 7:30", for example.

If I buy them at noon, I am afraid ithey will losehave lost their freshness when I take them home after a whole day's work.

It has been a while since the "fish and shrimp" were mentioned, so it's not that easy to immediately understand what "them" means.

I would probably write something like "If I buy the seafood at noon..."

When I am off work in the afternoonfinish work, it is already 5:30.

Or "When I get off work"

The phrase "in the afternoon" doesn't really fit because "5:30" is too late for the afternoon.

You could say "When I finish in the evening, it is already 5:30"

If I buy them at that time, it will be very late whenby the time I get home.

Yours wasn't wrong, but I suggest a phrasing that I think sounds a little bit better.

According toBecause of this daily routine, I don't have enough time to go to the farmer's market, so I haven't bought my mom fish and shrimp yet.

We would not use "according to" here

This morning I suddenly feelt I am too stupid-because thatere is an easy thing to do.

Now it is 5:22 in the morning, and I am going to get up and go to the farmer's market to buy them.

Need a conjunction between independent phrases (or a semi-colon)