How do you get the yoyo to spin so long?!
Throw hard, go fast and clean. That’s all I can think. This is really the only style where the yoyo helps significantly.
You can’t let your string rub the side of the yo-yo. You can also try getting a yo-yo that has more of an H shape like the Shutter.
Really, it’s the same way you get great spin times on vertical tricks: Keep everything in line, and practice, practice, practice. And yes, using yoyos with low walls helps a bunch.
The more you practice, the better you’ll get. There’s no real special trick to get you better. One day you’ll be struggling to string together just two horizontal elements, and a few months from then you’ll be wondering what elements you want to pack into 20 second horizontal combo.
So yeah. Practice, practice, practice.
Keep it moving. The momentum will help it spin.