Changing Enterprise Manager 12c Default inactive Timeout

Oracle Enterprise defaults to a timeout of 45 minutes . Depending on the organization or security policies you might want to change that to a lesser amount of time or in my case a longer period .
To check what the timeout is set

em@emap1>./emctl get property -name oracle.sysman.eml.maxInactiveTime
Oracle Enterprise Manager Cloud Control 12c Release 2
Copyright (c) 1996, 2012 Oracle Corporation.  All rights reserved.
SYSMAN password:
Value for property oracle.sysman.eml.maxInactiveTime for oms All Management Servers is null    null = default of 45 minutes

After you have checked the value . you can change it

/u01/app/oraem/oem12c/oms/bin
em@emap1>./emctl set property -name oracle.sysman.eml.maxInactiveTime -value 90
Oracle Enterprise Manager Cloud Control 12c Release 2
Copyright (c) 1996, 2012 Oracle Corporation.  All rights reserved.
SYSMAN password:
Property oracle.sysman.eml.maxInactiveTime has been set to value 90 for all Management Servers
OMS restart is required to reflect the new property value  

This will set the inactive time to 90 minutes . you will need an OMS bounce for this to take effect. Please ensure that whatever value you set meets your requirements and the security requirements of your company