The Senate sits starting at 6 p.m. this evening, and it is expected they will immediately begin debate on the government’s decision. It is possible the Senate could respond by night's end, potentially wrapping up the back and forth by the time the House of Commons adjourns at midnight.
Or, if senators decide to push back and insist on some of the changes that the government has turned down, it could be some time before the showdown concludes.
This legislative back and forth is all that stands between Bill C-45 and royal assent. Once it passes, the government will declare the date that legalization will come into force, expected to be sometime this September.