I have seen a thread on Battle.net, attributing the information to some other site. The information can be obsolete, as it seems to date back to 2.0.6.
All buffs are separated into several classes. Buffs in the same class are additive, classes are multiplicative.
Class A : regular buffs/debuffs/skills
A1 : Self buffs towards sheet dps - Glass Cannon, Hexing pants, MW, Familiar, BH-SS etc.
A2 : Most classical debuffs towards mobs - Strongarms, EE, Cold Blooded etc.
A3 : Every skill damage except Hydra - MM%, BH% etc.
Class B : elemental & pets
B1 : Elemental damage %
B2 : Pet % (MoJ and Enforcer)
Class C : elitist affixes
Damage dealt to elites / beasts / demons / humans is increased by %
Class D : Bane of the Trapped
Class E : Zei's Stone of Vengeance
Class F : Audacity
Class G : Hydra damage %
Hydra damage - unlike all other skill%, Hydra is not in the buff/debuff class A.
So, your final damage bonus would be
A*B*C*D*E*F*G, A = A1+A2+A3, B = B1+B2
So, in your question BoT is definitely multiplicative with Time Warp (it is with everything), the question is - which other buffs you already have in class A, that would decrease Time Warp's effectiveness. I am playing a Del'Rasha Wizard, so I always have +100% Meteor damage on Nilfur's Boots. Thus, Time Warp adds at most 7.5% to my damage.