This had been taken as Bug by VMware Support which is fixed in New Release 5.2
55734
[Provisioning/vCD] A programmed time out of 10 minutes occurs when provisioning a vApp
that requires an extended amount of time to fini
sh cloning. To resolve th
is issue, a new vCloud
activity timeout global property, Activity Task
Timeout, was added and affects the timeout for all
vCloud activities, such as inventory data co
llection, power options, and provisioning. The
default is 30 minutes and can be changed
by the vCAC administrator as required.