Hello Gert,
Welcome to the world of DirectRT and MediaLab! We are happy to hear you our using our software and are here to support your use.
When using a sound file for a stimulus, you should enter a "0" in the Time column if you want DirectRT to play the sound and proceed immediately to the next stimulus, like your video. If you want a delay before the next stimulus occurs, then you should enter the length of that delay in the Time column in milliseconds. So you will want to enter the number of milliseconds that you want to pass before each clip should start to play during your video file.
Jason Reed
Empirisoft Software Support Specialist