Any Tips on Time of Day and Day of Week optimization?

I'm wondering if any one has any time of day and day of week optimization tips for working with Campaign Monitor.

We do a lot of A/B subject line testing and feel like we are learning a lot from it.

I gather that the general wisdom is "deliver the campaign when the subscriber is attending to her email" and there are a lot of tips on when this might be, but generalizations like this only go so far, it always comes down to the habits of the actual subscriber population.

For time of day testing would it make sense to split a campaign into segments and send half the list at say, noon and half and 3pm and compare results?

For day of week testing would it make sense to similarly split a campaign and send half on Wednesday at noon and half on Thursday at noon?

How would I go about creating my own "random half of the list" segment?

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