windows has the win32 time service inbuilt... normally you would use group policy for configuration, but in your case - since you have no domain, you'll have to set things manually.
on the master server, you can use net time /setsntp:
on the other servers you can use net time /setsntp:
see this short article if you want more detail - http://windowsitpro.com/article/articleid/22123/configuring-an-authoritative-time-server.html