Checkpoint during Backup Can database process make automatic checkpoint when I'm in process of copying files during

ALTER DATABASE BEGIN BACKUP;


and     

ALTER DATABASE END BACKUP;


You can assume that process of copying files will last for very long time.
It somewhat begs the question of why not use rman for your backups instead of user managed backups.  rman has been the robust solution since at least 9i, and here we are with 12c being mature.