Three options for me:
1) Drive, usually takes about an hour from memory.
2) Walk to Twyford station, train to Reading, train to Twickenham, walk to stadium. I think about an hour and a half, again from memory.
3) Drive to Windsor, train to Twickenham. About 90 minutes total.
Return journey is usually worse as trains are overloaded or late, and car park is jammed.