require 'spreadsheet'
Spreadsheet.client_encoding = 'UTF-8'
book = Spreadsheet::Workbook.new
sheet1 = book.create_worksheet

book.add_format Spreadsheet::Format.new(:number_format => 'DD.MM.YYYY hh:mm:ss')

row = sheet1.row(0)
row[0] = "Date.new 1975, 8, 21"
row[1] = "Time.now.utc"
row[2] = "DateTime.new 2008, 10, 12, 11, 59"
row[3] = "DateTime.civil(y=2009, m=2, d=21, h=19, min=20, s=13, of=0)"
row[4] = "Date.new"
row[5] = "DateTime.now"

row = sheet1.row(1)
row[0] = Date.new 1975, 8, 21
row.set_format 1, Spreadsheet::Format.new(:number_format => 'YYYY-MM-DD hh:mm:ss')
row[1] = Time.now.utc
row[2] = DateTime.new 2008, 10, 12, 11, 59
row[3] = DateTime.civil(y=2009, m=2, d=21, h=19, min=20, s=13, of=0)
row[4] = Date.new
row.set_format 4, Spreadsheet::Format.new(:number_format => 'YYYY-MM-DD hh:mm:ss')
row[5] = DateTime.now

book.write 'test,' + rand().to_s + '.xls'