Is this prophylactic done by blowing and wiping on the body only at bedtime?

The permissibility of reciting the adhkar (remembrances) and seeking protection with them, along with exhaling (blowing) after recitation, has been established for when one goes to sleep and for ruqyah (exorcism/healing through prayer). This is based on the hadith narrated by Aisha (may Allah be pleased with her) that when the Prophet (peace be upon him) went to his bed, he would blow into his cupped hands while reciting "Qul Huwa Allahu Ahad" (Surah Al-Ikhlas) and both Al-Mu'awwidhatayn (Surah Al-Falaq and Surah An-Nas). Then he would wipe his face and whatever he could reach of his body with them. He also used to do this when he complained of an ailment or illness.