Thank you for your investigations! Right now, it's about 23:30 CET and the webpage is still unreachable. That's why I'm currently using a VPN connection (via UK) to write this reply.
Problems usually start in the region of 17:00-17:30 (CET) on working days and won't recover during the entire evening. On weekends, problems arise even earlier during the afternoon. We have a large number of users here, who are reporting the same issues in the Swiss Geocaching Forum. Most of them are Cablecom customers.
My IP is not static but operates in the same CIDR:
inetnum: 178.82.0.0 - 178.83.191.255
netname: CABLECOMMAIN-NET
descr: Cablecom GmbH
descr: DHCP Scopes
descr: Zuerich
country: CH
remarks: *************************************************
remarks: For spam/abuse, please contact abuse@cablecom.ch
remarks: E-mails to the persons below will be IGNORED!!
remarks: *************************************************
admin-c: LGI-RIPE
tech-c: LGI-RIPE
status: ASSIGNED PA
mnt-by: MNT-LGI
created: 2010-03-08T08:50:17Z
last-modified: 2012-07-03T08:10:21Z
source: RIPE # Filtered
Greetings
Ralf