You can be received at any time. In recent years, it has become customary to receive converts in a group after an RCIA program at the Easter Vigil, but converts who have had private instruction or for some reason aren’t part of an RCIA program are received whenever they’re ready.
In my parish, four are coming into the Church, all women this Easter vigil. Three are canidates, one will be baptized. Plus also I think sometimes a parish if it does not have an RCIA program, will send people who are interested in coming into the Church to a parish which has one.