So contrary to expectations, Albus did use his resources (ie: Gina and Aval) to research his own spell and in regards to the Demon King. And it did connect back somewhat with Auro and her dimensional magic. I guess there were some loops where he confided not only in Aval (I feel that was always a given) but also Gina with her connection to her master. Which means there was basis on why the speed run had to happen (as seen in the previous chapters)
I also think people are getting misunderstandings why Albus didn't use this earlier. First off, he just found out this spell's location. It was this current timeline specifically where the bard told him where it was, even if he was aware of it in the 16th loop. And second, it's the biggest last resort because the cost of using it is his life. He won't have a second chance after this and thus, won't be able to save Fiona if it fails.
Which does make me wonder, has Auro attempted it but instead tried to change it and thus had her body frozen instead? Maybe that'll be the key to reviving Albus!