While we get plenty of insight into all other subjects Harry took, the professors and what their lessons are like throughout the books, we do not see any Astronomy lessons happening, nor are the lessons or their timings ever mentioned. All we know is that Astronomy was taught by Prof.Sinistra, and that they had their lessons at the Astronomy tower.
Harry's Astronomy OWL exam is split into two sessions - theory in the morning, and practical exam at 11 pm so it would be conducive for stargazing.
Did the practical lessons happen during the night as well? Are the students exempted from curfew for these lessons? Are there any snippets in the books that I probably missed, regarding how and when these lessons took place, and who was good at it, or enjoyed it?