ffmpeg -ss 00:00:00.000 -i turtle.mkv -t 00:45:00.000 -c copy out.mkv
To cut out a section, just split it before and after the section to cut, then create a file with the filenames in it and run concat:
:: Create File List
echo file file1.mp4 > mylist.txt
echo file file2.mp4 >> mylist.txt
echo file file3.mp4 >> mylist.txt
:: Concatenate Files
ffmpeg -f concat -i mylist.txt -c copy output.mp4