We use the present continuous when the decision has already been made prior to the question being asked.

They are all correct. The first two sentences mean exactly the same thing. However, the 2nd pair of sentences have slightly different time meanings. That is because "going to (do something)" always implies future events or plans. "WHAT did you say you are doing tonight?" "I am going to go to the cinema with Ed." "I'm going to go..." implies the FUTURE (even the immediate future). "I'm going to the cinema..." could also mean the PRESENT. So it could answer the question, "What are you doing right now?" But it could also answer the same question above about future plans. It is a continuous tense. The future is a little tricky in English. You could also say, "Tonight I plan to go to the cinema with Ed." There are even times when you can use the simple present to express future plans: "Tonight I go to the cinema with Ed." Usually this is used to talk about planned or scheduled events... imagine someone reading their schedule: "This afternoon I meet Fred, tonight I go to the cinema with Ed, tomorrow I fly to New York..."

In your first example, the questioner would use "are leaving" if they were already aware of the planned departure, but not of its exact time. I imagine in your second example, you have a typo but intended to draw a distinction with "I will go to the cinema with Ed". You would say that to show that it's your voluntary decision and your intent to go sometime, which has not necessarily been scheduled yet. If it has been scheduled, especially if it's imminent, use "I’m going to go to the cinema with Ed".

Both can be used in the first sentence. "What time are you leaving tomorrow"- is more appropriate when the person you are asking this question has already made a decision. All of these can be used as well: What time will you be leaving tomorrow? What time are you going to leave tomorrow?What time are you going to be leaving tomorrow? Same goes for the second one (someone correct me if I'm wrong), both can be used as well. My advice is to keep it simple and just use the "I'm going to the cinema (store, mall, party) with Ed" . :)