That sounds like DNS redirection. Perhaps the DNS servers are slow responding to dslreports lookups. The "only late at night" probably indicates that the DNS info is in cache on your DNS server at other times.
That's what your description looks like from here. -- AT&T Uverse; Zyxel NBG334W router (behind the 2wire gateway); openSuSE 12.1; firefox 14.0.1