Sort by time and relevance means sorting will be done by time interval
such as today, last week, last month etc, within this group
results will be sorted by relevance so you typically get recent most
relevant posts first.
Sort by Relevance will sort by relevance, and
if relevance found to be the same newer results will be displayed first.
Sort by Time, asc, Sort by Time, desc will perform sorting by data
ascending or descending without taking relevance into account. This is
used best with exact phrase matching.