How can we set length limitation for the lines containing both single/double charaeters and line feed in a timesstamp?

We  have the following rule for the EN to JP subtitling translation: 55 half-byte characters/line, 2 lines in a timestamp.

By the length limitation settings of the Studio (2021), the length seems to be calculated like LEN function of Excel (counted one for a double-byte character) and
when including a line feed to be two lines in a timestamp(segment), all the characters in the segment are conunted.

So we must check the length outside the Studio, such as Excel or text editor.

We expect that a double-byte character should be counted as two and to check the length per line.
Is there any good tool or plug-in to easy to check the lenghth for above translation rule?

Best regards,