A few things from my testing in this dungeon:

1. Sidon doesn't like to spawn in certain positions. I find that standing in larger spaces with no enemies nearby will prompt him to spawn sooner - he won't spawn if there isn't much room for him to spawn.

2. When you're doing your first terminal, he will not walk to you. This means if you're doing a strat like ascending into one of the terminals, it will not work because he will stand still, talk about the terminal, and never walk to you.

3. Whistling does not do anything

4. Some runners have said turning the camera away (or zooming in and looking at the ground) will force him to spawn faster, but in my own experience I don't think this does anything either. I do it sometimes anyway, but I haven't noticed a difference

5. Ultimately, the speed that he spawns is random

I'd recommend watching the Water Temple in my All Dungeons PB, and you can get an idea of the places I stand in order to ensure that he spawns. I use Mineru to dupe while waiting for him at the first terminal, but he will spawn here anyway as long as you stand in the same spot.