I keep Rejuv and LB up on him the whole way to our base.
Simple enough. Or is it?
You want the LB to bloom when your FC is running low on HP.
So, you can't let it tick down to 2-3 seconds - If you are attacked, 3 seconds worth of damage will result in over healing.
BUT, 10 seconds is a long time to wait for that big heal, so, you don't want to keep refreshing it.
Generally, I refresh when there are 4-5 seconds left on my LB.
What about you other druids?
To each his own. I personally find 10 seconds to be a long time to wait for a direct heal. If you need a "big" insta-heal, use swiftmend or nature's swiftness+HT, and that would buy your bloom a few more seconds (assuming you aren't specced into refreshing LB with nourish/HT/RG).
*shrug*