Here's the link to the Catholic Encyclopedia.
I think the most helpful portion is here.
"The baptism of desire (baptismus flaminis) is a perfect contrition of heart, and every act of perfect charity or pure love of God which contains, at least implicitly, a desire (votum) of baptism. The Latin word flamen is used because Flamen is a name for the Holy Ghost, Whose special office it is to move the heart to love God and to conceive penitence for sin. The "baptism of the Holy Ghost" is a term employed in the third century by the anonymous author of the book "De Rebaptismate". The efficacy of this baptism of desire to supply the place of the baptism of water, as to its principal effect, is proved from the words of Christ. After He had declared the necessity of baptism (John 3), He promised justifying grace for acts of charity or perfect contrition (John 14): "He that loveth Me, shall be loved of my Father: and I will love him and will manifest myself to him." And again: "If any one love me, he will keep my word, and my Father will love him, and we will come to him, and will make our abode with him." Since these texts declare that justifying grace is bestowed on account of acts of perfect charity or contrition, it is evident that these acts supply the place of baptism as to its principal effect, the remission of sins. This doctrine is set forth clearly by the Council of Trent."
It seems that the "moment of perfect contrition" might be the answer to your inquiry.
May God bless you (and may your Honda run well.):D