Heering Cherry liqueur is made to an 1818 recipe from Danish Stevns cherries, harvested in August. The fruit is crushed with the stones, giving Heering...
I agree with Dave, I think the maraschino cherry syrup would be an okay substitute, particularly at just 1/4 oz. I think adding a teaspoon of Cynar or Averna, if you have one of those, will balance out the sweetness while adding the herbal component that the syrup is missing.