The rule about 30 seconds.

Hi. Today I will try to tell you about a one rule. I think it is very helpful.
I call it - The 30-second 30 seconds rule.

A core of the rule is to spend 30 or 60 seconds to write a basic idea after every important conversation or end of reading.
It will help you to remember basic idea or sense.

The second paragraph is okay gramatically, but it might sound more natural to say something like:

The idea is to spend 30 to 60 seconds writing the main idea of every important conversation or reading.

The rule about 30 seconds.

Hi. Today I will try to tell you about one rule. I think it is very helpful.
I call it - The 30 seconds rule.

A core of the rule is to spend 30 or 60 seconds to write a basic idea after every important conversation or at the end of reading.
It will help you to remember the basic idea or (help you make ) sense of it.