Nous avons assez de temps.

Because assez de is a quantity expression, and in French quantity expressions are normally followed by de + noun, not an article.

So:

• assez de temps = enough time
• beaucoup de temps = a lot of time
• peu de temps = little time

You would not normally say assez des temps here.

Here, assez means enough.

So assez de temps means enough time.

Be careful: assez can sometimes feel like quite or rather in other contexts, but in assez de + noun, it clearly means enough:

• assez de patience = enough patience
• assez d'argent = enough money

Both are possible.

• Nous avons assez de temps. = more standard or formal
• On a assez de temps. = very common in everyday spoken French

In modern spoken French, native speakers often use on instead of nous for we. But nous avons is completely correct and very common in writing and careful speech.

A careful pronunciation is roughly:

Noo zah-von zah-say duh ton

A few points:

• nous sounds like noo
• avons sounds like ah-von
• assez sounds like ah-say
• de is often a light duh
• temps is pronounced like ton with a nasal vowel; the final ps is silent

There are also liaisons here:

• nous avons → the s in nous links to the next vowel: noo-zavon
• often also avons assez → ah-von-zah-say

Because time is being used here as an uncountable noun, just like in English.

• assez de temps = enough time

French often uses singular nouns after quantity expressions when the noun is uncountable:

• beaucoup d'eau = a lot of water
• assez de travail = enough work
• trop de temps = too much time

Yes, but it does not mean exactly the same thing.

• Nous avons assez de temps = We have enough time.
• Nous avons le temps = We have time / We’ve got time.

Le temps often means there is time available in a more general sense.
Assez de temps stresses that the amount of time is sufficient.

Because after assez de, French uses de directly before the noun.

Compare:

• Nous avons du temps. = We have some time.
• Nous avons assez de temps. = We have enough time.

So the quantity expression assez de replaces what would otherwise be an article.

Yes. If the following noun begins with a vowel sound, de becomes d'.

For example:

• assez d'argent = enough money
• assez d'eau = enough water

But with temps, there is no contraction because temps begins with a consonant sound:

• assez de temps

Avons is the present tense of avoir for nous:

• j'ai
• tu as
• il/elle a
• nous avons
• vous avez
• ils/elles ont

So Nous avons assez de temps is in the present tense: We have enough time.

Yes. Suffisamment de temps also means enough time.

• Nous avons assez de temps.
• Nous avons suffisamment de temps.

The second version can sound a little more formal or explicit, but both are natural and correct.

The most natural negative is:

• Nous n'avons pas assez de temps. = We do not have enough time.

Notice that:

• ne ... pas goes around the verb
• avons becomes n'avons because ne shortens to n' before a vowel

So:

• affirmative: Nous avons assez de temps.
• negative: Nous n'avons pas assez de temps.

Normally, this is the standard word order:

• Nous avons assez de temps.

French does not usually rearrange this the way English sometimes can.
You could change it for emphasis in special contexts, but for normal use, keep this order:

subject + verb + quantity expression + noun

So this sentence is a very typical and natural structure.