AD inter-site replication time

2 question:
1. what should be a good sync time betwee sites (i have a site in Ny, washington, va, etc)
2. There is a ntds object in my AD that is trying to sync between a DC in washington and a server that does not longer exist, can i delete that ntds knowing that there is no other entry of that server in the AD, no in the users and computer and not in the DNS server

thanks