call your pastor and make and appointment to discuss your situation and learn about what is involved. If you are speaking of an unbaptized adult there is a period of inquiry first, which can take, weeks, months or even years depending on the person. Only when that person is ready (discerned together with the catechist and the pastor) to formally ask for the faith does he enter the catechumenate through the Rite of Acceptance. The catechumenate, the longest period of formal study and spiritual formation, is designed to last the minimum of one calendar year, from Lent to the beginning of Lent the following year.
The rite of acceptance may be celebrated several times during the year, as often as their are candidates ready for it. But the Rites of Christian Initiation are quite specific, and particular law of each dioceses specifies the time period required. It may take longer in some parishes if they follow a school year time-table (obviously, since 4-5 months are lacking) instead of a year-round schedule (which is preferred.) for some persons the catechumenate may take longer because of their personal situation, resolving doubts and questions that arise etc. A person should not be admitted to the catechumenate unless they have come to the point where they are ready to ask for the gift of faith, and have resolved all other canonical issues that would stand in the way (usually marriage/annulment issues).
If you are speaking of a person who has already been baptized into the Christian faith through another denomination and now is seeking confirmation and Eucharist (preceded by first confession) that is an individual judgement make with the person, the pastor and the RCIA catechist as to how long and how much preparation they need. For instance someone with a good scriptural background and knowledge of basic Christian belief may be much closer than a baptized Catholic who is essentially uncatechized (none or very little knowledge of the faith, bible etc.).
ideally RCIA is a year-round process and people are admitted to inquiry classes at any time, and receive the rite of acceptance or rite of welcoming when they are ready. I can tell you in our parish you would already have missed several months and it would be very hard to be ready by Easter (or Pentecost for baptized adults). But the “class” is year-round based on a syllabus that follows the Catechism, with scripture each week relevant to the lesson topic, and people can join at any time. We have “inquiry” sessions (much more informal) after each class for new people, so they can ask all their questions without getting the planned lesson off track.
please meet with your pastor without delay and find out where to begin. Welcome home.
the proper forum for RCIA questions is Spirituality, by the way, so check out the discussions in progress there.