This depends a lot on the computer speed and memory size. Usually a 2 1/2 hours recording and a file size less than 4 GB should be the high limits. A new recording should be initiated after this.
Recommendations from the developer of WM Capture for fixing audio/video sync problem:
WM Capture offers two video compression formats: MPEG-2 and Windows Media Player 9.
Both formats can be used to capture full motion videos (movies, music videos) or static videos (documents, pictures, browser windows) at high quality. MPEG-2 consumes less CPU power and is recommended for capturing full motion, larger size videos. Windows Media should always be used when capturing static videos.
Unless your computer is a dual core try to resize full motion recording windows to less than 1/4 of the screen.
If you use
Universal Audio Driver :
The Universal Audio Driver should be used on XP computers if your sound card does not allow recording. Some of the XP computers purchased in 2007 and thereafter do not provide audio recording options.
Before enabling this option close the browser or any media players. Open WM Capture first, then open your browser or media player.
Universal Audio Driver has limited use and may require some manual tweaking when capturing the computer screen.
The audio and video cannot always be synchronized if the video is interrupted by commercials, buffering or other events that may cause the audio stream to stop. If these situations can be detected WM Capture will Pause recording. You should manually restart the recorder. To eliminate some of the audio interruptions disable the Windows sounds. Click "Disable Windows Sounds" and select "No Sounds" in the Sounds scheme.
In some cases, a user specified delay should be inserted in the audio stream before recording begins. Usually the delay should be set between 500 and 5000 milliseconds.
My additional recommendations:
1. Disable active scanner of your antivirus if you use one.
2. Close all applications that are not required when recording.
3. Disable "Windows Media Player Network Sharing Service" and any other Windows services that you don't use, but which eat lots of your CPU resources (Make sure you know what you are doing).