$timestamp uses the total count ($count_samples + $count_contribs) as the number of days in the past to use as the starting point for the installation.
$count_samples includes 2 instances of "installer_timestamp()" that are not actual sample posts. The actual function name and once that gets reused foreach( contributor ). "minus 2" will help us :)
$count_contribs counts the number of elements in the contributors array.
$backdate is how far back we pushed the starting point, or the second half of $timestamp = ( time() - ( ( count_samples + count_contribs ) * 86400 ) );
$max_per_item_spread is the maximum real delta between time stamps, accounting for the 2 instances of installer_timestamp() that are not applications of a time stamp. This will, by design, be greater than the number of seconds in one day.
$ave_per_item_spread is simply the max minus 2 hours in seconds, which would be the average between it + or - 7200 :)
$fixed_entry_delta is the float rounded down to the next whole int value. We need that to make sure that the most recent item is always in the past.
This function modifies timestamp by a fixed amount of time +/- 2 hours, so the "worst case" math has to have the latest entry in the past. If the "coin toss" always comes up heads and the random addition is always 7200 we can now calculate backwards to find what the minimum fixed amount of time needs to be.
NOTE: using $timestamp inside if( $fixed_entry_delta === NULL ) ensures we never get closer than a day to right now.
