We all know investment bankers like nothing better than working through the night on an M&A deal, but the effects are more often evident in the queues at the coffee machine the following morning than in their written work.

Not so for a bunch of Goldman Sachs bankers in South Africa. Their advice letter to the board of Gold Fields, the South African gold producer they are defending against a takeover from Harmony, began dated November 1 but wasn't finished until November 2.