This library makes it easy to fetch a timestamp from an NTP timeserver. In order to use this library you will need the UDP libraries from:

http://bitbucket.org/bjoern/arduino_osc/

You will also need to modify the library to allow enough space in the buffers for the NTP packets. Open up UdpBytewise.h and change these lines:

#define UDP_TX_PACKET_MAX_SIZE 32
#define UDP_RX_PACKET_MAX_SIZE 32

to this:

#define UDP_TX_PACKET_MAX_SIZE 64
#define UDP_RX_PACKET_MAX_SIZE 64