Actually you need to hold up during gorm glas, before you link the 5C. If your timing is correct, you should get the 5C out before your jump starts.
j9 portion means, jump forward, specifically. Because jumping straight up won't work.. and the djBC vs djAB I believe is for corner, as jBC would push to far out of the corner to land the j623A
At first, the timing for that combo seems retarded, but, it's really not that hard.