Best time to visit hitachi seaside park

Is it a good time if i plan to visit hitachi seaside park between this 3 april to 7 april 2019? Or is it still early to see flowers there? Tq in advance

Visiting the Hitachi Seaside Park during spring usually the best time is from late April to early May for nemophila. Last year was early and full bloom occurred during mid April.
https://hitachikaihin.jp/info/post-50125.html

Another great time to go there is during autumn from late Sept to mid Oct for Kochia.

It depends on the type of flowers and what time of year they are coming into bloom. When at their peak, they can be spectacular. But between flower seasons, there is little to see and really might make you feel disappointed.
You also might consider visiting Kairakuen in Mito along the way. It is perhaps the least interesting of the traditional Top 3 gardens in Japan (except during the ume season), but worst case scenario, your day won't totally be a waste.

If you have the image of the Nemophila (Baby blue eyes) flower carpet on your mind, then your dates might be too early, as the blooming peaks in late April (https://rove.me/to/japan/hitachi-seaside-park-flowering). But it's better to avoid the time of the Golden Week when all the Janapese have a few days off, so the Park gets rather crowded.
However, if your dates are fixed, I would suggest checking the flower calendar of the Hitachi Seaside Park (https://en.hitachikaihin.jp/flower-calendar.html). It seems you can spot lots of daffodils in the West entrance area in early April. Hope that helps!