How little delay must I put from 23.38 to 25 fps?

A delay won't work for this. At 0.0 seconds, both the audio and video are perfectly lines up. You sped up the video by 7%. So at 1 second, the audio is 70ms behind the video. At 2 seconds, the audio is 140ms behind the video. At 3 seconds, it's 210ms behind and so on. You need to actually speed up the audio in order to fix this.