Record Subsection means that the device will automatically save the recording files in a period time you set. You can set it as 0/30/60/90/120/150/180/210/240/270/300/330/360Minutes.
The default is 0, it means the recording will be only saved after you switch the button to SAVE. So if you continue recording 200minutes, then the recording file will be in 200minutes length time.
When you set the record subsection in 30Minutes for example, then when recording, it will automatically save a recording file in 30th minutes, and then continue new recording. That means if you continue recording 80minutes, then after you finished recording. You will find that there are 3 recording files in it, the first and second recording file are both in 30minutes length, and the third recording file is in 20minutes length.