Hi Bongani,
As stated in the answer "When running a cutover migration, you must change the DNS MX record before your final synchronization run. Doing so will ensure that no mail will be routed to your on-premises Exchange server after the mailbox migration is complete."
You decide based on your specific situation to your environment. The have given you scenarios (seen below) of how to make these types of logical decisions:
If this is helpful please accept as answer or upvote.
Best regards,
Dillon Silzer | Cloudaen.com | Cloudaen Computing Solutions