I agree that the documentation could be improved.
According to this post:
raw data storage is available with the Plus plan.
I think that this is how it works, but I may be wrong…
If raw data storage is not turned on, the data received by the database is buffered and stored for 1 minute. Once that minute has elapsed, the data values received are averaged and written to the database.
I believe that this means that there will always be a delay of up to one minute between the data being sent to the Blynk server and it being available to view on the graph, unless raw data is used - but I may be wrong.
Pete.