I think Shevek was right about "nocturnal lucubrations" being redundant. The core idea in lucubration is that it is work done by lamplight (note the root luc-, from the Latin word for "light"), hence work done at night (the related, more common English expression is "burning the midnight oil"). While it is true that the word has come to mean intense mental work, as Mia points out, it seems a shame to lose that image of a person working at her desk into the wee hours, which seems, to me at least, intrinsic to the word. Another thought: the word lucubration is often used ironically (because it is in itself a rather pompous word) to mean deep complex writing (probably written by desk lamp through the night) that is ultimately beside the point or so erudite as to have little practical purpose.
Well, not necessarily. It could refer to any intense, laborious, and time consuming mental work that occurs either by day or by night. Initially, it might have had your suggested connotation, but the uses shift as the time passes, and I believe it now encompasses both of these meanings.