When I plug my Pi in and boot up, I am able to connect over the air with SSH at 192.168.1.100 (static IP address set in /etc/network/interfaces).
However if I boot up my Pi and leave it for 1-2 hours or longer, when trying to connect to my Pi with SSH at the same address, I always get the SSH error
Network error: Connection timed out
It seems as though the WiFi may shut down on the Pi after no useage for a certain period, however looking at the Pi physically, the lights seem the same as they are when directly booting up - Flashing WiFi Usb and other solid PI board LEDS.