OK, that makes sense I guess. I added this exception because when the hr_frametimes are defined [below](https://github.com/nipy/nipy/pull/278/files#L0L162), they start at 0 without inferring the actual frametime minimum. I agree with you  that the frametimes should be offset to reflect temporal interpolation, but it wasn't at all clear  from this function that it's up to the caller to handle that offset.