Now you can start a crontab with the tmutil startbackup command to kick off at your own schedule. with the --auto tag to make the system behave like if it were TM that called it itself
Not sure about the whole database file, but TM does have a locking mechanism. It's not that the entire backups becomes inaccessible though. It may limit writes, but it's mostly just to make sure that TM itself doesn't have two concurrent writes to the same database.