Feeding once a day

Question
When is a good time to switch from one feeding a day to two? We feed our 15 month old yellow lab at 8am and again around 5pm.  If we switch her to once a day I am worried that she will be hungry in the evening.  Will she? Is there a good way to transition?

When we switch her to once a day, will she poop less than she does now?

Thanks for all your great advice.

Answer
Today is the second day of no dinner for our 6 month old Lab.  We had been giving our older lab a snack when we fed the young one.  I have had to endure some major staring the last couple of evenings.  They will get over it.  Most Labs are always hungry.  Many are over fed.  Here is a link to a good illustrated guide to maintaining ideal body condition, http://www.puppychow.com/products/popup_body_condition.aspx

Not much hope on the poop.  The only thing you can do is feed a concentrated, meat based chow.  When we switched to Pro Plan from regular Purina, it did make a big difference.