The appointments displayed in the calendar on the platform already take into account the different time zones of you and your mentee.
This means that if you are in Berlin and enter an appointment for 4 pm, your mentee will see this in their time zone - for example 5 pm in Beirut or 8 pm in Kabul. The green dot in the calendar indicates that you both are free at that time - each in your own time zone.
Attention: Make sure that you are talking about the same time zone when you set a date at the end of your session.