yes there is a rule
for Catholics the rule is canon law
if you marry outside the Church you have voluntarily excommunicated yourself, and divorced yourself from the sacraments, including marriage. you do not just decide to convalidate months later at your convenience. you will have to go through whatever it takes to reconcile with the church first.
that the sacraments mean so little to you, which means you are prepared to reject the centrality Catholic life which is Jesus’ presence in the sacraments, indicates you are sorely lacking in basic knowledge of your faith, and your first priority should be to seek that knowledge, in prayer.
It is insanity to attempt marriage, with all its demands and sacrifices, without the presence of Jesus Christ. To try and carry out the promises of marriage on only your own strength is to court failure. Marry in the strength, protection and grace of Jesus Christ, and give love a chance.
if money is an issue, forget the big lavish reception and expensive accoutrements, buy attractive clothes you can wear again, and marry in before, after or during a regular weekend or daily Mass, you won’t even have to pay for use of the church and hall. or cough up the minimal donation for use of the church, marry and invite as many people as the church will hold, and have relatives serve cake, punch and finger foods in the parish hall.
if you care more about the outward non-essentials–the band, the hall, the glamor, the dress, the party–than about the convenant of marriage, you are not ready for marriage in any case.
if you are in a country like Mexico or Japan that does not recognize a religious ceremony, the rule is different, you marry civilly and then marry in the religious ceremony immediately afterward, without living together as man and wife in between, so as to avoid the sin of so doing. but you do not allow months to elapse. In cases of true need–immigration situations, military deployment–the bishop is directed to do everything possible to expedite the marriage, so make sure the priest understands the situation. Tsuwano describes the correct procedure when there must be a delay between the legal marriage and the religious sacrament.