"Every country has it's autumn celebration. Does the southern hemisphere have a harvest time festival in April or may?"
Not really. In Australia and New Zealand we have ANZAC Day on the 25th of April, but it's not a harvest festival; it's more like Veterans Day.
People have tried to get Christmas in July happening, to have the Christmas style festivities at a time of year when the temperature makes sense. (Have you ever tried eating a hot roast dinner in 40°C [104°°F] heat, with a side of high humidity?)