I'm constantly surprised by how much trouble films run into with that step, or rather, the difference between films made by experienced pros and films made by those with lesser experience. The last two features I worked on, one was in post-production for over 2 years and the other had been in post for well over a year before audio-post even started. All caused by directors/producers whose "vision" during pre-production was limited to production, and we're not talking about nano-budget films here.
I don't expect this to be much of a problem for you though, it's a short not a feature and from what I know, you have considerable pro experience in this regard. If you do run into any issues or uncertainties with the audio-post/music side of things, don't hesitate to shoot me a PM.
G