This is the link to the whole piece, performed on piano with notation
The arrows and sixteenth-notes (or sometimes eighth-notes) indicate the time offset between measures in the upper and lower staves.
They don't have musical meaning in themselves. They're guideposts to help interpret the varying positions of the barlines between the two staves.
In the below image, from 0:20 in the video, it shows that the upper stave's 7/16 measure begins first, and the lower stave's 3/4 measure begins offset by one sixtheenth from the upper stave. This offset continues into the shift of the lower stave to 4/4. The upper stave's measure of 3/4 begins one sixteenth after the lower stave's 4/4 measure begins.
The situation is a bit more complex in this next image from 0:28. Here, the offset between barlines of each stave is greater. For example, the upper stave's 7/16 measure begins five sixteenth-note pulses before the lower stave's 3/4 measure begins.