gmt begin time
gmt set FORMAT_DATE_MAP o FORMAT_TIME_PRIMARY_MAP Abbr FONT_ANNOT_PRIMARY +9p
gmt basemap -R1997-01-01T/1997-07-01T/0/2 -JX10c/2c -Ba1Of1o -BWSen
for value in off +1o -1o; do
    gmt set TIME_IS_INTERVAL=$value
    echo 1997-03-05 1 | gmt plot -Sc0.2c -Gred
    echo 1997-03-05 1 $value | gmt text -F+jBC -D0c/0.2c
done
gmt end show