Using simple past with and without specific time

I know that simple past is used to talk about:

1. Completed action in the past (with specific time)
2. A series of completed action
3. Duration in the past
4. Habits in the past
5. Past facts or generalizations

And as I understand that you should not use a specific time with last four uses but you must use a specific time for the first use to be grammatically correct, according to:

https://www.englishpage.com/verbpage/simplepast.html

But, I still see some sentences without a specific time, such as These sites:

https://www.grammar.cl/english/past-tense.htm

I went to the beach

https://www.studyandexam.com/past-simple-tense.html

I ate an apple

https://www.grammarly.com/blog/simple-past/

We won several medals

And more.

Now I am so confused when to use specific time or not, then when should we use a specific time?

No, there's nothing that states, "...you must use a specific time for the first use to be grammatically correct," not even your link, which states, "The simple past... is used to show that a completed action took place at a specific time in the past." That doesn't say that specific time in the past has to actually be explicated. You don't have to say when that specific time in the past was to use the simple past, and when you leave it unstated, then the simple past nonetheless conveys or shows that that specific time in the past exists.