Well, as the problem is predictable at a specific time everyday, I would suspect your location / environment and something that happens at that time.
As a Network / System Admin, I had a similar situation in an old school one -- everyday at 3pm the Head of School would lose all Wi-Fi accesss. I looked at everything I could imagine that might be a problem, even though nothing suggested any connection to the repeatable time of the issue.
Finally I went and simply sat outside her office and waited for 3pm, and then it was obvious -- at that time of day, school was generally dismissed ... so the administration building would fill with parents and students with various requests, etc. On the list of most common Wi-Fi radio interference is ... the human body. This coupled with a poorly installed access point resulted in a predictable interruption to the Head of School's Wi-Fi access.
A very common practice in home or consumer environments (apparently even in old schools too), is to place the Wi-Fi access points (and routers) at convenient locations, often on furniture 2'-4' in height. This means that anyone walking by causes radio interference, to some degree. In the school situation, I simply mounted the access point on the ceiling (where it should've been initially), and the problem resolved.
So, are your access points as high as they might be to avoid human interference?
