Beyond The Elastic Limit: An Epic Fable by Howard Loring is a great time travel story.  The setting is a cosmos in which God, unsatisfied with the way mortals were handling things, stepped in personally with a clear Mandate to spread life throughout the galaxy and with the technology to do it.  This occurred, however, in the distant past of the Golden Age of Primus.  The story begins near the completion of the Mandate and involves holy war, heresy, and an interesting twist on the end times, or perhaps a new beginning.