2. The "Time spent per visit" metric requires at least two "hits" to your site from a visitor in order to be included in the metric and doesn't consider how the visitors actually came to your site. See http://marketing.adobe.com/resources/help/en_US/reference/metrics_time_spent.html for detailed information about how "Time spent per visit" is calculated. "Search Keywords-All" only considers visitors that came to your site via a search. A visitor that came to your site by directly typing in the URL would be included in the Time spent per visit calculation but not in the Search Keywords calculation.
2. The "Time spent per visit" metric requires at least two "hits" to your site from a visitor in order to be included in the metric and doesn't consider how the visitors actually came to your site. See http://marketing.adobe.com/resources/help/en_US/reference/metrics_time_spent.html for detailed information about how "Time spent per visit" is calculated. "Search Keywords-All" only considers visitors that came to your site via a search. A visitor that came to your site by directly typing in the URL would be included in the Time spent per visit calculation but not in the Search Keywords calculation.