No Internet on Laptop in Evening but Phone OK

This is a strange one and its happened for the last three days in a row.

At around 10pm to midnight (roughly) the two laptops in our house can't load websites but during that time our phones can still access the WiFi and load websites. The laptops can connect to the internet but can't load anything.

I've tried turning off the WiFi modem, turning off all the devices apart from one laptop.

If I click on the 'Troubleshoot problems' option on the network icon in the task bar it says there is no problem.

The phones are definitely connecting to the network and not using 3G or similar.

The laptops are Windows Vista and Windows 7.

Any ideas?

Thanks!