I don't understand what you are referring to Bigbazz? If you use WOTB during the physical buff, how does that give you two rotations of the physical buff? And why would you want to use Rend during the lightning buff? Most people that use Rend use the physical rune.
rend does not snapshot, meaning it changes its damage if your dps changes. So if you put your physical rend on while lightning buff and it switchs to physical buff, then rend will also be buffed for that duration.
If you put your rend on in "physical buff" then you not only waste time not whirling, but also waste time not having rend active when physical buff starts. If you put it on while "physical buff" and "physical buff" ends, then rend will also deal less damage from that point on.
...edit for bad info... above is correct.