I did get an answer. The timeout in Virtual Center is set at 15 minutes. You can make it shorter, but not any longer. In vReplicator you can run the backup without using VC. It connects to the source host through VC. It connects to the target host directly. All of timeout errors were for one VM on the target host, so this solution was perfect for me. I'm not sure if the samething will work for VCB.
Ron