Run-time preview should use a default period timeslot 00:00-24:00

Current Situation

When assigning a calendar to a run-time without specifying a period, then future execution dates are not displayed with the run-time preview.

When assigning a timeslot for the period 00:00-24:00 then the run-time preview displays future execution dates.

Desired Behavior

When no period is assigned to a run-time using a calendar, then the default period timeslot=00:00-24:00 should be used and future execution dates should be displayed with the run-time preview.