[susan53]

At/In/On

1. In + period of time : at a certain moment during a long period of time : in July, in 2004, in the evening, in the night and for named events occurring during a period of time.
I went to Rome in July / in 2004 = period of time
I often wake up in the night. = period of time
In that Night of the Long Knives... : named event occurring during a period of time

2a). At + specific times/ named events occurring at a specific time - no article : at 3am, at Christmas,

I often wake up at 3am. = specific time
I went to Rome at Christmas = named event occurring at a specific time
I'll see you at Consultation Night[/i] = named event occurring at a specific time


3. On + specific day : on Thursday, on December 4th, on my birthday, on the (day of the) Consultation evening, on the (day of the) Night of the Long Knives

I'll see you on Thursday
I'll see you on (the day of) the Consultation Evening
It happened on the (day of the) Night of the Long Knives


4. At + article + place/event : at the party, at the conference, at the meeting, at the Consultation Evening (understood as At the meeting which will be held on that evening) - notice that here at no longer refers to the time but to the location :

I'll see you at the meeting.
I'll see you at the marketing meeting.
I'll see you at the Consultation Evening (meeting).

So it all depends how the speaker perceives the time reference and the event.