hi,
on that site, jesussecret.org, it says "... theologians argue that Jesus died on Friday evening yet he rose or came back to life early Sunday morning. For, it is mathematically impossible to get three days from Friday evening to early Sunday morning--it's impossible."
It isn't impossible. Friday is the first day, Saturday is the second, Sunday is the third. Three days. Jesus rose on the third day.
As for the metaphor of seeds and plants, there are MANY metaphors in the Bible. (Jesus is the true vine, He's the lamb that was slain, etc.) I think the ability to see metaphors is a gift from God and it's something we should use often. But that doesn't mean everything in the Bible is merely a metaphor.
Ask Jesus to help you see, not only mathematically and metaphorically, but also through His eyes.
:-)