1-      Log into the vsphere web client
(Flex)
2-      Go into “host and cluster” view
3-      Select the vcenter server
4-      In the right pane, choose “Configure”
5-      Choose advanced vCenter Server
Settings
6-      Choose edit
7-      In the edit box, search for “timeout”
8-      Edit the “vpxd.http.clientIdleTimeout”
value 
8-      We set it at 32400 (value is in second and equal to 9h) so you login once a day into it.
9-      Click “Ok”
