I had similar problems to yours Senior P. though I am on a Windows machine, using ADSL2 and a router. Huge amount of trouble shooting by Telstra/Bigpond etc. and it turned out to be excessive 'noise' coming from a set top box that my next door neighbour had for a huge satellite dish antenna he had bought to receive up to 32 non English speaking programmes! As soon as the box was off everything back to normal. Maybe a piece of electrical equipment near you comes into play around 11.00 and 23.00?
Sorry LateArrival, can't help.