Remember to heat it up till it is piping hot not just warm. If you don't heat chicken thoroughly you may get food poisoning. Also beware, the time it will take to reheat the chicken mixture the vol en vants will possibly over cook. Personally I would make them on the day, or make the filling the day before, cook cases on the day and then you can reheat chicken safely in the pan.
Please don't!! Make them on the day or use a different filling. You have to be so careful with chicken - it isn't worth taking chances. E-coli is horrific - I speak from personal experience (someone else's reheating).
Angie is correct, so long as the chicken is heated thoroughly to piping hot, any harmful bacteria will be killed and it will be perfectly safe to eat.
There is a common myth that you should only heat food once to avoid food poisoning, but this is not true, you can reheat it over and over quite safely so long as it is heating to piping hot!