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
5 Star Servants Tier List: Best Servants [5/9 updated!]
FGO Reroll Tier List [5/11 updated!]
How to farm EXP cards & level fast
How to unlock/maxing Irisviel (FGO Fate/Accel Zero Order event)
1-3 Star Servants Tier List
[JP] Halloween 2017 Event: Halloween Strike!
Best Craft Essence: Craft Essence Tier List
Nero Claudius (Caster, Summer 2017)
Elizabeth Bathory (Caster, Halloween)
Trick or Treatment
Talk on the Heated Sands
Piece of Year 2030 (A Fragment of 2030)