How long does an npc take to respawn in terraria?

I beat the WoF and lost my guide (yes i liked him) and now I have to search for recipes and stuff like that. I later found out that you need to make a room/house for him which I did.

Now how long do I actually have to wait until he respawns because I'm really needing him right now and I cant do WoF again because I failed last time and he's dead. Please help I need my guide back he was like a father to me...

Solution 1:

From the Terraria Wiki -

A killed NPC will respawn the following day and move back into its house (provided it still meets the requirements).

So as long as your guide still has a house he will respawn next day. Day begins at 4:30 AM but they can respawn at any time. Based off of my experience they usually come really early but they do come late sometimes.