The Speed Rune increases all of the crafting operations of the Blood Altar. The crafting speed (and speed that the progress is lost when empty) increases by an additive +20% per rune.
With some Netherite Scrap and some Intricate Hellforged Parts looted from the Demon Realm, you can double the power of your Speed Rune, increasing the crafting rate by an additive +40% per rune.
If you change your mind, you can undo the recipe in the ARC.