The cider is now bottled in 1 gallon growlers (which despite any debate involved in their use, seem to hold their Co2 and pressure fine), and has ~1.00 gravity. They came out pretty dry, and due to the type of apple juice I used, didn't come out with a lot of flavor. To compensate for the lack of flavor, and to both carbonate it and sweeten it, I thought of adding apple concentrate to each of the growlers a few days before the wedding, allowing the yeast to metabolize a partial amount of sugar, while still leaving a considerable amount of residual sweetness.
Now my question is concerning the amount of apple concentrate juice to use, and how long prior to the wedding it should be added to end up with an eventual medium between sweetness and Co2. The wedding is on August 1st.