Finally I did it
15 zimbra-servers: one master (ldap,mailbox,mta,av\as,spell,logger) in head office and 14 slaves(ldap,mailbox,mta,av\as,spell) in branches, successfully upgraded from 7.0.0 OSS to 7.1.3 OSS.
Version of servers:
Release 7.1.3_GA_3346.RHEL5_64_20110928134520 RHEL5_64 FOSS edition.
Release 7.1.3_GA_3346.RHEL5_20110928134520 RHEL5 FOSS edition.
So, 18 hours - everything works fine. I hope that will continue the same way