The first couple of nights are usually the slowest in the specialty restaurants. As word spreads throughout the cruise, or as the clock is ticking, they fill up more. That is probably the genesis of the first night bonus.
A Bad Day At Sea [with power] Always Beats A Good Day At Work
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014