By our calculations, you should look at sowing Sumter about 14 days after your last frost date.
Hybridized by Clemson Agricultural Experiment Station; Year of Registration or Introduction: 1973. Patent now expired, so this also may be considered OP. See trivia below for explanation. 1
Plant patents on hybrids only last 20 yrs, this is no longer patented, ever since 1994. Therefore, seeds have been saved (legally) and OP versions of this cultivar exist from such seedsaving. :)
Sumter Hybrid
1 http://davesgarden.com/guides/pf/go/70644/