Any prayer of simple faith requesting salvation through Christ is honored by God. Thirty years ago I was at my cousin's wedding reception and my nephew sat next to me at the dinner table. I asked him if he wanted to know God? He said yes, so I explained salvation to him and prayed with him at the dinner table in front of all my non-believing relatives. I felt the burden of sin lift off him at the same time he did and he said, "I feel lighter!." I live in Texas and he lived in California so I did not get to see him again.
He moved to the Midwest where he had a terrible marriage, from which he finally divorced. He met a Christian woman and moved to Oregon where they married. He began following Christ at that time. My brother, his father, died Christmas day last year and I saw him again at my brother's funeral. We talked and he thanked me for praying with him at my cousin's wedding. While he did not have discipleship, during his first marriage, he was aware of God's help in his life.
If I could have been there to help him in discipleship it would have been better, of course, but when we pray with people to accept Christ, Christ accepts them and takes responsibility for them. We are not abandoning new believers because we are giving them over to the One who cares the most for them. But God does not violate our free will and the choices we make. Thus there are consequences that God works through with us when we choose poorly. It is for this reason we see long or short discipleship times. We determine the speed of our discipleship by our choices.