Source → data → def → json → npc_definitions.json → find the impling npc id and lower the respawn time.
Example:
Code:
{
"id": 7903,
"name": "Kingly impling",
"examine": "An impling who likes the word 'kingly'.",
"combat": 0,
"size": 1,
"attackable": false,
"aggressive": false,
"retreats": false,
"poisonous": false,
"respawn": 1100,
"maxHit": 0,
"hitpoints": 0,
"attackSpeed": 0,
"attackAnim": 0,
"defenceAnim": 0,
"deathAnim": 0,
"attackBonus": 0,
"defenceMelee": 0,
"defenceRange": 0,
"defenceMage": 0
},