Agents can be in any time zone and any location. As long as they have network connectivity to the Enterprise Manager (MOM and Collectors), the time zone and location are not a factor.
MOM and Collectors don't have to be in the same time zone. However, if logging into the GUI via webstart workstation, that could affect your reporting. The server that you log into using Workstation will display the time that you are currently in. For example, if your MOM is in the Pacific Time Zone and you are in the Eastern Time Zone, your Investigator will show the time in the Eastern Daylight Time zone. To set the time zone in the workstation to the time zone that you want to be displayed, see the section below in the documentation (link below).
Time Zone Display in the Web Start Workstation
Start the Workstation - CA Application Performance Management - 10.5 - CA Technologies Documentation