For any given meteor shower in a given year (e.g. Quadrantids, now) where can I see a rough prediction of how many days it will last? For a given shower the rate hitting the Earth's atmosphere versus time is usually a peak with a width of a few days, though there are some exceptional unicors. 

Is there a place where I can view this envelope? 

The context here would be to have some idea for a given year of a given shower how much less intense it would be one, two, or three days before or after maximum. I'm not looking for something precise or location dependent, but just to get an idea how critical it is seeing it on the "best" night versus a more opportune night.

Is there some place to go to see some predictions of many of these envelopes in order to look up a given one, or to see which ones are narrow and which ones are wide?
The International Meteor Organization publishes an annual Meteor Shower Calendar.
The PDF document for 2020 predicts a Quadrantid peak on January 4, 08:20 UT, and says:


  The peak is short-lived with an average duration (full width at half-maximum, FWHM – that is the period with ZHR above half of the peak level) of about four hours.


Unfortunately it only gives peak durations for a few showers.