-condition requires to read the original mboxes completely, which can
-be slow. However, header conditions are checked first to read the
-bodies only for mails which fulfill them entirely.
+condition requires to read the full mail from the original mboxes,
+which can be slow. To speed things up, all the header conditions are
+checked first.
+.TP
+\fB8h\fR, \fB24h\fR, \fB48h\fR, \fBweek\fR, \fBmonth\fR, \fBtrimester\fR,
+and \fByear\fR selects mails received during the last 8, 24, 24, 48, 7
+* 24 hours, 31 * 24 hours, 92 * 24 hours, and 365 * 24 hours respectively.