The sunset is ephemeral. It's night before you know it.
a. 1. Beginning and ending in a day; existing only, or no longer than, a day; diurnal; as an ephemeral flower. 2. Short-lived; existing or continuing for a short time only. ´Ephemeral popularity.´ V. Knox. “Sentences not of ephemeral, but of eternal, efficacy.” Sir J. Stephen. Ephemeral fly (Zoöl.), one of a group of neuropterous insects, belonging to the genus Ephemera and many allied genera, which live in the adult or winged state only for a short time. The larvae are aquatic; — called also day fly and May fly.