4th Singularity London: Southwark free quest is the best AP & time-saving location to farm Homunculus Baby. You'll get about 3x Homunculus Baby by spending 190AP. Evil Bone is also dropped.
Here is a list of servants that need Homunculus Baby to perform Ascension and Skill Up.
Rashoumon event (Ibaraki Douji event)
Murder at the Kogetsukan
Inheritance of Glory
FGO Reroll Tier List [5/11 updated!]
Device Transfer Guide
How to farm EXP cards & level fast
Best Craft Essence: Craft Essence Tier List
Talon of Chaos (Claw of Chaos)
Glassful Sweet Time (Glass Full Sweet Time)
Minamoto no Yorimitsu (Berserker)
Mysterious Heroine X (Assassin)