I wouldn't have dared to defy my teachers

[Yankee]

Hi Nessie

It is generally the case that any given idea can be expressed in a number of different ways. The person could have said "I didn't dare" in order to simply refer to a 100% real past. However, if someone says "I wouldn't have dared", then some sort of theoretical aspect has been introduced into the sentence. It is often not particularly important to know exactly what the theoretical condition is, or it can just be assumed from the broader context. In your sentence, the usage is similar to a type 3 IF sentence. I would simply interpret the unspoken condition to be something very general, i.e. similar to "If I had been in your shoes" or "If things had been different". It means not only "I didn't dare" but also "I wouldn't have dared even if the situation had been different from the one I really had".

Regarding 'today':
In a nutshell, since the person used the simple past tense (!!!!!!!) to report the act of defying a ban, you should not understand the word 'today' to mean 'nowadays'. It happened earlier today. It's as simple as that.
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"Nearly all men can stand adversity, but if you want to test a man's character, give him power." ~ Abraham Lincoln