Fit the cucumbers, dill and garlic into a 1-quart Mason jar. In a small saucepan, combine the vinegar, sugar, salt, mustard seeds and 1 cup water. Bring to a simmer, stirring until the sugar dissolves. Pour the hot mixture into the jar with the cucumbers and let cool to room temperature. Cover and refrigerate for at least 2 hours and preferably overnight. The pickles will keep, refrigerated, for up to 2 weeks.