No. The "5 seconds" that I was taking about is not a /proc/sys/vm/dirty* number. It is ext3 (and presumably ext4) specific.
It defaults to 5 seconds (JBD_DEFAULT_MAX_COMMIT_AGE) and can be changed by the "commit=nn" mount option.
That many seconds after a journal transaction has been opened, it is closed and flushed - if it hadn't been closed already.
It is the metadata that is written to the journal - inodes, free-block bitmaps, directory names etc.
The file contents are handled differently for different settings of "data=".
ordered: data that relates to the metadata in flushed before the metadata is written to the journal
writeback: data is written according to /proc/sys/vm/dirty* rules
journal: data is written to the journal with the metadata.
I'm not sure what the default is today. If you create then delete a file, the data will not go to disk, except possibly for "data=journal". But the metadata will.