'Mal' is an occasion or event, as in 'zum ersten Mal' meaning 'for the first time', or 'einmal' meaning 'once'. 'Zeit' means time as in time passing e.g. 'eine lange Zeit' is 'a long time' There's one more to add to the list - 'Uhr', meaning 'hour' is how you talk about the time on the clock. 'Wieviel Uhr ist es?' means 'What time is it?' If you think about it, these are actually three different concepts, and it's slightly odd that English uses the same word for all three situations.

die Zeit is the time as in what you see on the clock aka the duration of something or how long it lasts. e.g, 'I kann nicht gehen, weil ich keine zeit habe ', 'I cannot go because I have no time ' das Mal is the instance, e.g 'So sehe ich zum ersten Mal die Monde des Jupiter und die Ringe des Saturn. ', 'So I see for the first time, the moons of jupiter and the rings of Saturn' Another way I see it is by looking at the word mal in other words such as Damals as 'Back then' as you're referring to an instance