Formerly all departures were interpreted as death. Nowadays the symbolism is much more of a new beginning. We are leaving our old life in order to undertake something new. When someone in our lives leaves us, we may dream of departures and the grief that parting causes.
In certain circumstances, to dream of wanting to leave but not being able to suggests that there is still further work to be done.
To be conscious of the time of departure might suggest that we are aware of a time limit within an area of our lives. You may also like to consult the individual entries for airport and departing.