Because minute is the plural form.
So:
This often surprises English speakers because minute looks like the English singular form, but in Afrikaans it is plural here.
Here it functions as a predicate adjective/complement after is.
So the structure is:
Afrikaans learners do not need to change the form of genoeg here. It stays genoeg.
Because none is needed.
Compare:
In your sentence, the plain amount of time is being stated, so no article is used.
The normal word order here is:
That is the most neutral and natural form.
You can change the sentence for emphasis or by adding other elements, but Afrikaans still follows its usual verb-second pattern in main clauses. For example:
So yes, word order can change, but the original version is the standard simple pattern.
A rough learner-friendly guide:
The hardest word for most English speakers is genoeg, especially the g sounds. If you cannot make them perfectly yet, that is normal.
By itself, it normally means ten minutes as a stated amount.
If you want to make it clearly approximate, Afrikaans usually adds another word, such as:
So Tien minute is genoeg normally presents ten minutes as the amount being judged sufficient.