Communications Lead for Legends of Runeterra, Dillon Buckner (aka A Small Man), just confirmed that we will see an extra Vault that opens tomorrow (July 9) rather than a full nine days, like originally stated in the patch notes.

Quote From Dillon Buckner
Hey folks, update regarding the Vault move to Thursdays with this patch—this week we'll actually have a short two-day vault that unlocks this Thursday to make the transition, then continue with 7-day vaults normally after Thursday. Sorry for the confusion!