Recurrence by Date and Time requires refresh in order to have an extra field for a new date
cal version 1.5.3
In Backend, when you create a new event with a Recurrence by "Date and Time" and the frame gets reloaded you can only add one date. In order to have another field for another date you have to save the current page and when it reloads you will find a new field you can enter another date in.
You should not save the current page when you want a new field, this should be added automaticly.