The bridge will now open from 11pm to 5.30am increasing the number of journeys by 90 minutes.
The new hours were successfully trialled and the structural monitoring confirmed the loads were within acceptable ranges.
Transport Minister Derek Mackay said: “Work to restore the bridge to its full capacity is continuing at pace and this is another step towards that goal.
“The HGV trial has been running for more than a week now and our careful monitoring shows that we can now allow more vehicles across the bridge.
“It means that more than 90 per cent of traffic has access to the bridge while the strengthening work is carried-out by our expert team. All indications are that we are on track for the full re-opening soon and we will continue to explore options to allow as many HGVs as possible to use the crossing in the meantime.”