What does this phrase mean: "in good time"?

[Oana]

Test No. incompl/advan-13 "Time Expressions (1)", question 6

I always like to get to an appointment in ......... time.

(a) good
(b) best
(c) fine
(d) clear

Test No. incompl/advan-13 "Time Expressions (1)", answer 6

I always like to get to an appointment in good time.

Correct answer: (a) good
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Could you please explain why this is the correct answer?

[Alan]

This means so that you have time before an appointment starts and you are not in a rush or late.
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[Vara]

Hello Alan,

why we don't use here "appointment in a good time"

[Alan]

Hi Vara,

There is no article 'a' in this set expression. 'A good time' would mean an enjoyable time.

Alan
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