Are my spawn conditions for the cicada shell wrong?

[Bilaz]

Hey guys, I've checked all the guides but I'm just not certain. I wanted to check if I got the conditions right for the cicada shell before I spend a whole other day trying to catch it.
So I went to a mystery island at around 11 PM on the 29th of august, I decided to go in the night because I couldn't find a single rainy day.
I landed on a random mystery island, it's not bad as the river is small but it's not perfect. I can't reset for bamboo island as I ran out of NMT. But it's fine I check the tiny area for any diving beetle or other spawns once the spawns on the main island part start getting low.
I cut down the palm trees and plucked every flower, and I've just been walking back and forth staring at fruit trees, and they keep spawning common stag beetles, I've been at it almost all my free time all day. Are these conditions ok? Can I just keep myself on this mystery island until I catch it (it'll stay 11 pm 29th of august forever right?)
Thanks so much if you can help!

Ninji's Mystery Tour Islands Guide

It's just island 0 in this one, I got rid of all flowers and palm trees, and all trees on that small bit on the other side of the river (I check it regularly but not the entire time)
I replaced all cedar trees with fruit trees because I can't see spawns well on cedar wood in the dark

 

[Skyfall]

I also did this too. Cicada shell is just extremely rare/low spawn rate. I feel your pain

 

[John Wick]

The only spawn condition is the month(s) they are available in.

Those Crook Mile islands aren't special.

When they were in season I saw plenty on my island.
You only need to look at the trees.

You don't need a guide.

 

[Bilaz]

Thanks!!!
Yeah I just have the island set up like this because I see way more horned dynastids and other stuff like this, so I figure I’m having more spawns!

 

[Crowsie]

When I was a kid you couldn't brush up against a tree in the late summer without knocking down a dozen cicada shells.
Animal Crossing will have you thinking they're as precious as gold. Don't give up, the spawn rate is just extremely, extremely low.
I was on the hunt for one throughout the entire season and only found one 3 days before they went away.

 

[Bilaz]

Thanks everyone!!
I found it and... got too close to the tree and... missed
D:
at least I know I can keep trying though