A few things from my testing in this dungeon:
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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.
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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.
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Whistling does not do anything
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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
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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.