You can eat at the Hostess of Fertility once a day to increase the multiplier, which should make it faster. Also, the formula takes into account the level difference between the player and the monster... If your character is level 3, a level 1 goblin will not do much.
Ah, no need to worry, I've been going to the tavern everyday for that multiplier meal. However, I'm still level one and at the "free 7 days" section so I'm grinding all my stats to S-rank(if possible) to make my playthrough as canon as possible for the main animated series storyline. So I'm making good use of my time to strengthen up, you know?