What happen in the R/3 system during the extraccion

Hi:

I would like to know what whappen in the R/3 system during the extraccion. In my company they told my that during the extraccion the documents that they are treating BW can't consider them to be transfer, so they are stopping operations during 2 hours to load data.

Is this true? Is there any place where i can see some technical information to corroborate this?

Thanks.

Points for helpful answers.