Question 1042673
This is a binomial (break/don't break) with very small probability of breakage and a very large sample with a constant probability of n*p=8 per 24 hours or 8*(5/24)=5/3 per 5 hours.  That is lambda. 
P=e-(lambda)*lambda^x/x!, where x is the number of breakages here.
e^(-5/3)*5/3^1/1!
=0.3148 probability of breaking in next 5 hours.
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To me, exactly 5 hours from now is an infinitely small point and therefore an infinitely small probability.  
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For 3 mirrors,
e^(-3)^(5/3)^3/3!
=0.0384
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Over a small interval, the probability of an occurrence is approximately proportional to the size of the interval. The probability of an event in a certain interval does not change over different intervals.
I would say the probability is 3/5 of the probability in the next 5 hours or 0.1889.