Downstream Receive Power Level : 6.75 dBmv is a wee bit high for an old ntl100 especially, but with you mentioning that it only goes off early evening it could well be a ubr issue (when everyone gets home from work & starts using the internet)
However, I noticed that your using Zone Alarm
Even the Ex NTL stopped recommending it because it caused so many connection problems. Try disabling/uninstalling ZA about 30 mins before your connection normally goes off & see what happens..
Dont suppose you have Norton AV installed as well by any chance..?