[1] When you say this in the evening, you should say: Allaahumma maa 'amsaa bee...: "O Allah, as I... enter this evening..."
[2] Whoever recites this in the morning, has completed his obligation to thank Allah for that day; and whoever says it in the evening, has completed his obligation for that night. Abu Dawud 4/318, An-Nasa'i 'Amalul-Yawm wal-Laylah (no. 7), Ibn As-Sunni (no. 41), Ibn Hibban (no. 2361). Its chain of transmission is good (Hasan), Ibn Baz, p. 24.