Length – if your callers typically wait 2 minutes at a time, then at least 2 minutes of programming should be the goal. The idea is to ensure the callers don’t hear repeated messages every time they call. A typical on-hold message is 4-8 minutes in length.
In a few simple steps you can have a customised sell on hold message in as little as seven days.

The problem, in my mind, is that every single one of these articles misses the point completely. Even if you implemented a call centre system that detected and automatically played someone’s all-time favourite music while they waited, a facility which is possibly not that far off, most music when played down the phone just sounds terrible. Butchering a song that someone actually likes is unlikely to improve the waiting experience.
Even if your wait time is short, don’t discount the power of hold music. OnSIP’s average wait time averaged 18 seconds last month, which is just long enough for the caller to notice that the instrumental music is pleasant, with enough character to prevent boredom, before our team picks up. When that’s the last thought in your caller’s head before speaking with your business, it’s likely to be a more pleasant conversation than it might have been otherwise.