"A apărea noaptea"
Translation:To appear at night
No, there are two distinct situations:
Vampirii ies noapteA - The vampires go out AT NIGHT.
Maria pleacă LA noapte - Maria leaves tonight.
In conclusion, when there is no "la" before "noaptea" (with a definite article), this expresses a general situation. On the other hand, the presence of "la" sets a specific time.
The above applies for "dimineața" (in the mornings in general) vs. "la dimineață" (tomorrow morning specifically).