Ok, you will need custom SQL - no getting away from that. Start to create an Interface property alert and copy the below query (notice it starts from a comma). Change the NodeID, InterfaceID and traffic volume values (example below is for 30 GB) noted in blue. The query below computes a running total for the day
,
(SELECT
InterfaceTraffic.NodeID AS NodeID,
InterfaceTraffic.InterfaceID AS InterfaceID,
SUM((NullIf(In_TotalBytes,-2)+NullIf(Out_TotalBytes,-2))) AS SUM_of_TotalBytesRecvXmit
FROM InterfaceTraffic
WHERE
( DATEPART(d,DateTime) = DATEPART(d,GETDATE()) ) AND
InterfaceTraffic.InterfaceID=209 AND
InterfaceTraffic.NodeID=150
GROUP BY
InterfaceTraffic.NodeID, InterfaceTraffic.InterfaceID ) TodaysTraffic
WHERE TodaysTraffic.InterfaceID = Interfaces.InterfaceID
AND TodaysTraffic.NodeID = Interfaces.NodeID
AND SUM_of_TotalBytesRecvXmit > 30000000000