Okay, so i went and made a video of the impossibleness
http://www.youtube.com/watch?v=JkbkgEuBlRkBasicly read the description. And as KlydeStorm pointed out; i have 5:17 ingame hours. I can't remember how the ingametime / Real Time goes.
And as shown in the video, even if i use L to Levitate, i'm still not going to make it.
(When i get to Castle its 14:11)
So unless someone finds a new strat on how to get to hyrule castle drainhole, i'm either going to wait to daytime or go and get ZL before going to Zora's River
More testing is needed