Drain the cherries, reserving 1/4 cup of the juice., Combine the 1/4 cup cherry juice and sugar in a medium-sized saucepan, and cook over medium heat until the sugar is mostly dissolved (it should be more liquid than granular), 2 to 3 minutes., Add the cherries to the pot, and bring the mixture to a boil. Cover the pot and reduce the heat so the liquid is simmering., Simmer for 45 to 55 minutes, checking on the cherries and stirring them gently every 10 minutes or so, until they're slightly wrinkled and firm when you touch them with a spoon. At this point the syrup should have reached about 235°F, known as soft-ball stage., Remove the cherries from the heat, uncover the pan, and allow them to cool to room temperature., Remove the cherries from the pot with a slotted spoon or strainer, transferring them to a parchment-lined baking sheet or plate., Use cherries immediately, or store them in an airtight container in the refrigerator for up to 6 months.