In the U.S. and Canada, generally only large commercial and industrial entities have time-of-use rates.
Because hardware costs remain the most significant cost of mining yet, even if a time-of-use rates were accessible, mining is still (at current levels) profitable during peak pricing (in most areas) so it wouldn't make economic sense to shut down during those times.
This was described here as well:
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http://www.bitcoinminer.com/post/2858427974