The lagoon show is always about 10 - 15 mins before park closing. It’s the “finale” for the evening.
It may not happen due to weather. Also, before the hurricane destroyed the last lagoon show there were some days - like Mondays / Tuesdays when there was no show at all. I presume that was due to lower crowd levels and time off for maintenance.
Just check the App under the “Shows” tab.
