"We easily have enough time."
Translation:Nous avons largement le temps.
On principle, there is nothing wrong with it, except usage: the French don't say it that way.
expressions: "plus de, moins de, assez de, trop de, peu de" are constructed with "de" alone.
Is it just specifically here that one has to use "on" rather than "nous" or is there a general set of expressions where one has to use "on" in favor of "nous"?
"Nous" is 1st person plural whenever you want to express that the subject is yourself + at least one other person. However, in the oral and familiar French language, "on" replaces "nous" very often. Please note that "on" is 3rd person singular and therefore is conjugated like il/elle. In some cases you use "on" while it is not a replacement for "nous" but a non defined subject.
- "on a fait ça": you don't name the person having done that, you don't know who did that, so the real subject may be yourself, a third party or your counterpart: "I did that" or "he/she/someone did that" or "you did that", or as I said before: "we did that".