Error filling print... Font 'Arial' is not available to the JVM. See the Javadoc for more details.

Проблема решилась так:
apt-get install ttf-mscorefonts-installer
Копируем все ttf файлы из папки /usr/share/fonts/truetype/msttcorefonts в директорию нашего любимого jdk - JAVA_HOME/jre/lib/fonts
Перезапускаем iReport, открываем наш документ и всё как надо.)

Отличия Calendar.HOUR_OF_DAY от Calendar.HOUR

Calendar.HOUR = Field number for get and set indicating the hour of the morning or afternoon. HOUR is used for the 12-hour clock. E.g., at 10:04:15.250 PM the HOUR is 10.

Calendar.HOUR_OF_DAY = Field number for get and set indicating the hour of the day. HOUR_OF_DAY is used for the 24-hour clock. E.g., at 10:04:15.250 PM the HOUR_OF_DAY is 22.