The official independent FBI internal investigation on his conduct and recommended his firing was just completed and given to Sessions on Wednesday.
Sessions knows he has to to everything by the book, so that he can respond to media attacks on his character - which are inevitable - by pointing to official bureaucratic processes, like the coming IG report and this week’s OPR recommendation.
This is a crucial element to taking this seditious cabal out.
If Sessions got the report on Wednesday, Thursday firing would have been called rush to judgement without due consideration, so either way it would be spun then.