Is it permissible to begin the night vigil (Qiyam al-Layl) after the Maghrib prayer or between the Adhan for Isha and the Iqamah, or must it be after the Isha prayer, in order to achieve "whoever prays with a hundred verses will not be recorded among the heedless"?

The Hadith "Whoever stands with one hundred verses will not be written among the devout" has not been found. Perhaps the questioner is referring to the Hadith: "Whoever stands with ten verses will not be written among the negligent, and whoever stands with one hundred verses will be written among the devout, and whoever stands with one thousand verses will be written among the Muqanṭireen (those given a huge reward)." There is no objection to performing the night prayer after Maghrib prayer or between the Athan for Isha and its Iqamah.