The initial phrase seems to conflate several elements but leads to an interesting discussion. While sunflowers don't actually bloom overnight in the traditional sense, their growth and flowering process does have some fascinating nocturnal aspects.
On the fourth night, a city drone—programmed to extinguish any "unregistered light source"—detects the glow. Hikari and Yoru try to protect the flower. Yoru throws his sketchbook to distract the drone's sensors, while Hikari covers the sunflower with her own coat. The drone sprays a dark foam. The sunflower's glow dims, and it begins to wilt. himawari wa yoru ni saku ova sunflower ha yoru
Whether Himawari wa Yoru ni Saku was ever a real OVA may be less important than what it represents. In the collective imagination of anime fans, it has become a placeholder for every beautiful, sad, unfinished story — a sunflower that opens not to the sun, but to the quiet mystery of night. The initial phrase seems to conflate several elements
Thus, "Sunflower ha Yoru" directly translates to "Sunflower is Night." This is likely the subtitle or an alternative reading. An OVA with a dual title like: Hikari and Yoru try to protect the flower
Some users confuse this phrase with the Korean live-action film Sunflower (2006) or the Japanese indie film Himawari (2012). The addition of "OVA" might be a nostalgic mis-tagging by fans who remember a specific scene where a flower blooms in moonlight.