How do balloons work?

Hi guys, I'm going crazy for this thing and I hope you'll be able to help me T.T
I thought that balloons were spawning every 10 minutes, but it seems like they spawn when they want.

I was quite sure that they were sapwning at __:_4, because sometimes they used to spawn at the beach at that time, but then they stopped to show.

After that, I started to see balloon at random times... Sometimes they spawn at the beach at __:_6, sometimes at __:_5 and one day one balloon spawned at __:_2

And today I found a spawned baloon at __:_5 on the beach. After shooting it, I ran to the other side of the isle (it took like 30 seconds) and there was another balloon ready to leave the beach (and disappear). I was able to shoot it, so there were 2 balloons at the same time.

I really can't understand how thay works, most because even if I count 9-10 minutes from when the first balloon spawns, I can't find other balloons after the first one. I literally search through the entire isle, but any balloon shows...
I only find them randomly and it's sad because balloons give lots of useful stuff...

Do you guys now how all of this works and do you have any advice to not miss them?

Thanks in advice