Honestly, I don't want time travel anywhere near Mass Effect. It practically always leads to some inane predestination paradox, which hasn't been a clever plot twist since 1950's. Time travel stories tend to lead to cheap cop-outs, as anything that goes wrong, can, in principle, be corrected.
And it so happens, that if you combine relativity (time dilation) and faster-than-light travel, you lose causality (i.e. the principle that the cause must happen before the effect), which leads to a form of time travel. In that light I'd prefer that they just handwave time dilation away with space magic. It's not as if a real scientifc explanation exists anyway.