FiChai

Never heard of 回禮利是 to be given at time of sending invitation cards. Reasons are, how do you know if the guests would attend only the ceremony or reception or both yes or both not? How do you know how much money or gift they would give you, so by what percentage of the 回禮利是 should be calculated? If you just want to save some work and give a random figure to all guests, it won't be appropriate anyways and someone might get upset at the end.
That's why there are always "receptionists" act as gift record registers at guest sign in table, in order to mark down each gift by which guest, so you can have a better idea how to do the 回禮利是 afterwards if you want to.