Since one of the latest app updates, the e-mark updates date and time automatically. Make sure that you selected a date or time function in the editor. Then, send it once to the e-mark, the rest will be done by the e-mark itself. The e-mark can even be switched off in-between and will print the current date and time.
Please note that by removing the battery or having had a battery level of 0 %, the e-mark resets the date/time and will not print the right information any more.