Two alternatives.

The simple alternative is to create a table with one byte for each state the LEDS can have.
0x00 - all LED off
0x80 - one LED at top lit.
0x40 - have moved one step.
0x20 - two steps dow
0x10
0x08
0x04
0x02
0x01 - first LED have reached bottom of hour glass
0x81 - new LED starting path down
0x41 - one step down
0x21
..
0xFF - all 8 LED lit - time to start emptying it again
...

The next alternative is that you look at the above and see how you can convert it into loops. When filling the display, you loop through # numbers of LED. And an inner loop that moves the new LED down while there is space to move it one step further down. When the LED reaches the end (after 8 steps) or next LED position is already lit, then it's time to exit the inner loop and have the outher loop start with a new LED.

Nothing hard. But you must spend time trying to design the loops. It may be easier to do in C than in assembler. Or if you must have an assembler solution, you could prototype the solution in C and then rewrite in assembler when you have figured out what the loops are expected to do.