I killed Carhillion (Sorcery merchant) how long until his tombstone appears?

It's been hours and I've reloaded, quit, warped, etc multiple times but still no dice. Any clue on where or when his tombstone appears?

As of current knowledge the best and most efficient way of making tombstones appear is by Quit/Reloading until they appear. I have in personal experience had NPC's come back anywhere from the first reload (immediately after killing) to the fourth (also immediately after killing). Also be aware that the Tombstone locations do not completely correspond to the locations you killed them, and you may have to search around to all locations the NPC goes to.

He has two locations:

• No-Man's Wharf
• Majula

His tombstone in Majula appears quite fast (a couple of reloads for me), but I killed him in Majula.

I don't know what happens when you kill him in No-Man's Wharf: where his tombstone is going to appear.

This is not uncommon for this to occur for any of the NPC's, it's just more common for some rather than others. The general consensus is to quit and reload, wait up to 2 in-game hours (leave the area, don't just go AFK in front of the dead NPC), then return.

Also it is entirely possible that if you killed him in No-Man's Wharf, his tombstone could appear in Majula, as that is his final meeting place. Other characters that this occurs with are Ornifex (You find her in the Shaded Ruins, and the tombstone can be located in her shop in Brightstone Tseldora), and (I believe) Licia of Lindelt.

EDIT: His grave appears in Majula