If you're using DVDA-2, specify a 5-second introductory media clip which would play before your menu appears. A disadvantage to this is that there is often a pause or momentary black screen as the DVD player changes media from the intro clip to the menu.

In DVDA-3, you'd use a menu loop point to specify the time at which the menu buttons appear. In this case, you wouldn't use a separate introductory clip, you'd use a clip where the first 5 seconds represented the intro media and the balance of the clip would be your continuously-displayed menu.