Quick Warps
Quick warping is a way to shorten the animation on the warps between the Light and Dark Worlds. It saves 34 frames per warp, which adds up to about 12.5 seconds over a full Any% NMG run.
How to perform it
The only factor on whether a warp will have a quick or a slow animation, is the vertical position of the camera (in other words, the X coordinate of the left and right edge of your screen). For every eight pixels, there will be two that ends up being quick warps. Note that the Y coordinate (top/bottom of your screen) does not matter at all.
Since the camera follows Link around, you can usually use Link as a cue for this, but it's important to understand the distinction, because in certain screens, the camera can sometimes be offset by a pixel or more, making your Link cues not work.
Applications
You can find basic info for all the quick warps here: Krystal's Notesmash Quickwarps
Flute Quick Warp
To help with this I recommend using your menu to the mirror as a buffer to easily see where you are and how to adjust. If you are a god though, you can switch to the mirror prior to getting the shovel to save a couple of frames on that menu, and then get the quick warp bufferless.
The general QW area from right to left:
This is a bad pixel to the right of where you need to be (XP: 142)
I like to look at the tree to the right of Link as a cue here. There's a 1 pixel gap between the right root of the tree and the edge of the screen. Pretty easy to recognize.
Here the root is perfectly aligned with the edge of the screen. You can also still see a strip of grass above the root between the edge of the screen and the leaves in the tree. This 1 of your 2 good pixels that will get the quick warp.
Here the black border of the root is cut off some, but you still have a 1px gap of grass right above it. This is your 2nd good pixel that will quick warp.
Now you can't see any grass above the root at the right edge of the screen. This is a bad pixel that won't warp you.