Sound triggering issue in Keynote

Greetings Fax_Fax,

Thanks for posting in the Apple Support Communities!

It sounds like what you are experiencing may be expected to occur, but let’s check into this with you. To confirm we understood this correctly, you are attaching an audio file to each slide but notice a delay in the audio playing at the correct time. Is that right?

If we have that correct, you may want to consider adding a soundtrack as opposed to an audio file. If the audio file you're adding for each slide can be combined to be a soundtrack, this would allow the audio to play when the presentation starts in the order you prefer. For more details on using a soundtrack instead, check out the following resource. The information below can also be found here, and outlines that the audio plays only when the slide is showing in your presentation, which could be what's causing what you experience: Add video and audio in Keynote on Mac - Apple Support

Add video or audio

When you add a video or audio file to a slide, the video or audio plays only when that slide is showing in your presentation.

Do one of the following:

• Drag a media file from your computer to a media placeholder or anywhere else on the slide.

• Click  in the toolbar, click Movies or Music, then drag a file to a media placeholder or anywhere else on the slide.

Tip: To search for a music file, click the magnifying glass in the upper-right corner of the media window.

Click the Play button  on the media to play it.

We hope that's able to help with what you're looking to do.

Have a great day!