Your smart meter will measure the import and export values and report these in 30-minute blocks. So if for example you consume 1kWh from 09:00 to 09:15 then at 09:15 you start exporting (the clouds clear and it’s a warm sunny day, for instance) and export 2kWh from 09:16 to 09:30 then your bill will show both 1kWh consumption and 2kWh export in the 9:00 to 9:30 period. Your export amount is not deducted from the consumption amount.