I need to check a log.txt file if it is changed, so if it is than must copy XL.txt file
If it is not than must copy ML.txt file

The Idea of checking that is to copy log.txt to log1.txt and than
use fc command like
fc  log.txt log1.txt > nul
 if errorlevel 1 (goto C) else (goto D)

But problem is because log.txt fill up very slowly and as I see fc chek a file size and file size changes takes more than 10 minutes.

How can solve that problem to check if log.txt was changed last 5 minutes?
Maybe this might help you.  If some even happens only once every  ten minuets,  you should not be testing all the time because that will burden the CPU. Instead, you may schedule a task to be performed every ten minuets.
Here is a general discussion about the windows schedule thing for batch.
Run a batch file with Windows task scheduler (From stackoverflow.com)

Quote

... the same problem, but I found another solution without having to modify my batch script.  The only thing that I missed out is at the 'Action' settings - "Start in (Optional)" option.
Go the task properties --> Action tab --> Edit --> Fill up as below:
    Action: Start a program
    Program/script: path to your batch script e.g. C:\Users\beruk\bodo.bat
    Add arguments (optional): <if necessary - depending on your script>
    Start in (optional): Put the full path to your batch script location e.g. C:\Users\beruk\
Then Click OK
...

Perhaps  you did not understand. Batch does not have an effective scheduler. Wasting time in batch is a bad idea. Instead  you create a batch file that does what you want. It must be a cone time self-contained batch. No looping. It runs once and stops.

Start Task::
  For every ten minutes

Batch can do that very efficiently, Geek.

Code: [Select]:loop
echo ...
timeout /t 600 /nobreak
goto :loop