This is one area where there is no hard and fast rule because it depends on your business. If you're a dentist and your average patient waits 10-15 minutes before getting called back, you can create a much shorter playlist than an automotive repair shop, where a customer may wait 30-45 minutes to have their car worked on. So consider your average customer dwell time and then create a playlist that runs about double that length. That way, even when you’re running behind, your audience won’t be overexposed to the same, repetitive content.