I would say that is not that hard to do it, if he is an advanced 3d artist he might done it in 2 days even less
I m a 3d artist more as an environment artist so i would do it in max 2 days, about the grass you can make it in 30 min max, for example for our game i didnt slept for 36+ hours when we started the jam lol. You better check your story before say stuff like that dude :)