This is what Canon Law says:
Can. 851 The celebration of baptism must be prepared properly; consequently:
1/ an adult who intends to receive baptism is to be admitted to the catechumenate and is to be led insofar as possible through the various stages to sacramental initiation, according to the order of initiation adapted by the conference of bishops and the special norms issued by it;
Can. 856 Although baptism can be celebrated on any day, it is nevertheless recommended that it be celebrated ordinarily on Sunday or, if possible, at the Easter Vigil.
The Rite of Christian Initiation of Adults is designed to lead to Baptism at the Easter Vigil.
The RCIA says that baptized non-Catholics are not to have more imposed on them than is necessary to bring them to readiness for reception into full communion. For example, a well catechized Anglican may be ready to be received in 6 weeks and it’s not reasonable to expect this person to go through the same preparation as a non-baptized person. OTOH, a poorly catechized or non-catechized person might require just as long as a non-baptized.
The RCIA also stresses repeatedly that we have to be careful to treat the baptized differently from the way we treat the non-baptized. Dismissal, for example, should not occur with the baptized. Unfortunately, due to lack of catechists, both groups are often lumped together for everything and the baptized are made to wait far too long to be received into full communion.
A bad thing that has resulted from RCIA is what I call the “assembly line model”. Everybody starts RCIA in September or October knowing they will be rewarded for attendance by being baptized at Easter. That is not what the catechumenate is supposed to be. It should last at least a full year and should recognize that true conversion is a process that can’t be rushed and while one person may be ready for baptism in a year, another may take 3 to 4 years of catechumenate to be ready. Few parishes do that and that’s why we see dozens baptized at Easter but a few years later only a handful are still attending Mass on a regular basis.