I think the first problem is caused by timing issues. The axis is not yet updated with the new values in the moment you try to set the selection.
If all you want to do is to expand it from end to end then you can do:
-- Live demo --
This will ignore the actual dates and will set the selection from the first to the last category. Assuming 1000 categories or less.
As for the second issue, the "to" date must be larger than or equal to the end date of the last category. In this case the category ends at 2012-01-01 00:00.
I'm a getting a bit worried about the stability of the solution so far.
Please, do test for breaking changes to the private APIs on major releases.
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