If you are unable to set the system time from command line within a container carry out the following:
Shell into your Proxmox controller (houses the containers/VM’s. Then run:
vzctl stop 100 vzctl set 100 --save --capability sys_time:on vzctl start 100
Where is your Virtual Environment ID. Next, log back into your virtual environment and issue the following commands to set the appropriate time-zone for the Virtual Environment (VE).
vzctl enter 100 mv /etc/localtime /etc/localtime.old ln -s /usr/share/zoneinfo/Europe/London /etc/localtime
Now you can set the date and time appropriately.
date -s "20 MAY 2014 10:00:00"