I went back today, the flowers are mostly gone. The beautiful site that you were seeing in all the pictures from last week, you won't see any longer. You can see just a few flowers here and there.
For sure, I saw some poppies were withered when I visited at 6th , April, and it was reported by visitor that the flowers were starting to fade from middle of the month, I believe that most of the flowers are not in good condition caused by recent dry and hot weather.
It is difficult to predict when flowers will be in bloom. It is contingent on the weather, the poppies open in warm weather, and they close when it's cold. Best thing to do is check the weather the next few days and if it appears it will be in 70s, good chance there will be blooms. The reserve provides daily updates on their website, and I believe they do same in their Facebook and Twitter accounts.
Thanks! Your answer is awaiting moderation.