Adding a Time Offset to a Dynamic Field for Scheduling Appointments inside a Process

[Specific]

I am working on a process in which I need to add an appointment.

The "StartTime" is determined by a dynamic field. I want the "EndTime" to be 14 days after the "StartTime".
Is there a way to add a time offset something like "<OTRS_TICKET_DynamicField_TicketFreeTime4> +14d", or what would be the best solution here?