Also, I was playing around with Nature's Bounty and I noticed something interesting. After casting 3 rejuv's on just 3 targets, I get the Nourish haste increase (with current gear I'm at 1.6s cast time). This does stack with Nature's Grace as expected, bringing the cast time down to 1.4s (same as RG).
The thing is...if you cast 3 rejuvs on 3 targets, and then spam nourish, you actually keep the haste buff until the last rejuv wears off and even beyond. I casted 3 rejuvs on 3 targets (the last being myself). Even after the buff had expired on myself, my next cast was still 1.6 seconds for one cast.