The perceived render time represents how long the initial visible page takes to load. With usual text / image size ratios, this largely depends on the load time of the slowest image within the page's visible range.
Review the below link for more understanding.
To add on to that, with version 7 you would also be able to include visually complete time with UEM, please see this link for more details:
Thanks for your reply. We need to look into the perceived load time in Dynatrace. Could you
please tell us whether it is possible or not with the 6.5 version which we are using now?
Do we need to upgrade to the next version ?
The term perceived load time seems to me a Visually Complete & Speed Index for Real User Monitoring (RUM) which is available in the AppMon 7.0 release.
Below is the description of this feature.
Visually complete is a point-in-time metric that measures when the visual area of a page's content has finished loading. Visually complete timing happens substantially earlier than the typical page load time, and optimizing the visually complete timing is more valuable then optimizing other page load timings when targeting the user experience.