Underwater Long Exposure

I was looking at cameras and housings that would work to take a picture underwater that is longer than 30 seconds.  I have found the Sony RX100 III to be a very capable camera that also has an Ikelite waterproof housing to go with it.  My true desire is to make a long exposure in coral reefs and other places using scuba gear, but I think I'd first have to start with snorkeling.  I haven't snorkeled either, but I think this could all be quite interesting.  While looking online for anyone else who has done similar things, I found this guy's blog: www.amustard.com.  Hopefully I can make some of these soon!