Horocycle flow on the unit tangent bundle of a hyperbolic surface has non-trivial time changes, in fact obstructions to trivialization of a time change are precisely described in the work of Flaminio and Forni. In this talk I will discuss the work of Mieszkowski: trivialization of time changes for a 2-dimensional unipotent algebraic action on the manifold obtained from the product of SL(n, R)s factored by an irreducible lattice. I will then explain how this is used towards understanding perturbations of the action. This is joint work with A. Katok.