Here is CBS' "master press release" for Star Trek from July 18. (They also issued individual joint press releases with Netflix and with Bell Media.)
Star Trek International Broadcasters Set for New Star Trek Series
It sounds like CBS coordinated the timing around the launch of Discovery and tied the contract negotiations for the old series to that. Netflix was probably the big fish and Bell Media in Canada had very little control of the timing.
My guess is the contract took effect in September and will probably run for several years. They don't usually disclose the length of these types of contracts.