No, it is not true. dVS acts like a normal switch on an ESXi host, but can only be configured on the vCenter. THat means, you cant change anything on the switch unless the vCenter is back.
But, there is indeed a 24h restrict reg. dvs and vcenter. If a VM gives back its assigned port, it is blocked for the next 24 hours by default (it can be changed) http://vmetc.com/2010/03/06/24-hour-timeout-prevents-removing-esx-vnetwork-distributed-switch/