Hi,
It's not uncommon for people to see disconnection patterns like this. In most cases it's easy to fix though.
Generally you'll find that connection drops like this fall in to 2 types. Ones that are caused by something external causing interference and ones that are caused because the line is just sync'ing that bit too high.
First thing I would suggest is to check if there's anything else that happens at the time the connection drops, for example central heating switching on/off or street or other lights switching off. This can be common if it happens at a similar time each day.
I'd also suggest taking a look through this to see if anything helps:
http://usertools.plus.net/tutorials/id/13any incorrect wiring or filters could easily cause this, particularly if it ties in with something (e.g. an unfiltered alarm system phoning home).
If nothing there helps then I would suggest looking at or logging the router stats when the problem happens. In particular you are looking at the SNR figures to see if they decrease. If you do then it could as I say be sync'ing at just slightly too high a speed. Because of things like atmospherics and street lights and other factors that can cause "noise" sometimes the speed the line syncs during the day is just too high for the evening and the line drops and resyncs. If this is the case we can raise it as a fault with BT and increase the target SNR on the line to cause it to sync at a slightly lower speed to improve the stability.