This metric is not available in browser API. This is difference between user action start time and visuality complete time. Such calculation can be done only when you will export data to elasticSearch for example. There you can make calculations on index level which will give you answers. Agents by default does not make it. You can post product idea for this case.
thank you for your reply
The Start Render time is measured as the time from the start of the initial navigation until the first non-white content is painted to the browser display.
And I found it already implemented on appmon.
I guess with "Time to Start Render" you mean the webpagetest.org defined metric: "The Start Render time is measured as the time from the start of the initial navigation until the first non-white content is painted to the browser display. "
Dynatrace does currently not support this metric and it also can not be calculated by any of the existing metrics. The W3C specification group is working on more metrics and Chrome also has introduced some metrics in this area which we are currently evaluating. We plan to bring some of them to product as soon as we are sure that they will be supported for some time. Two metrics which will come are the W3C paint metrics: https://developer.mozilla.org/en-US/docs/Web/API/PerformancePaintTiming (but if you look at the end of the page, even they are not fully supported by all browsers).
Other metrics like: "First Meaningful Paint" which is available in Chrome for some time will not be introduced as Chrome will remove them again.