Auroras: is there any bump in frequency at certain times of night, or times of year? I'm trying to find out if there is a range of times at night, and/or days during the year, in which the probability of seeing an aurora is higher than average. 

The aurora section of the British Astronomical Association asserts that there's 
a correlation with season (higher probability near equinoxes), and a correlation with 'magnetic midnight'. 
http://www.britastro.org/aurora/

Are these assertions correct? If so, what is the definition of magnetic midnight, exactly?
Magnetic midnight occurs when the sun, the observer and the magnetic poles are in the same plane. This occurs around local midnight: In the USA it is about 1 hour before local midnight, in the UK it is about 2 hours before local midnight (local time is the time as shown on a sundial, with no adjustments for daylight saving etc)

The aurora season is the winter, mostly because at the high latitudes where aurora are visible, the sky is not fully dark between April and September.

Aurora are most likely during solar maximum, which occurs every 11 years (with a good deal of variability). Solar activity remains high for about 4 years. There have been maxima in 2000 and 2014 (the last cycle has been long and weak) The next is due around 2023-2025.