Migrations can easily be paused and then resumed on demand.
To pause migration, select "Cancel/Pause Migration". To resume, you can then click "Resume Job/Rerun Failures".
When the migration starts again, it will pickup from where it had left of, first running a quick check on the scan and mkdir stage results. You can start and stop migrations as often as you like.
Keep in Mind
Clicking "Start Migration" rather than "Resume Job/Rerun Failures" will result in the migration starting from scratch again.