Timestamp for running activity!

During an activity - press the Lap button on each change, then it will be marked as laps which you can review later by opening the tab at the bottom.

Or hover mouse over pace chart, it displays time and pace for selected point, so you can find it by looking for higher/lower pace.

thank you for your answer but i want to know the time when i did something

for example i start my workout at 10:30AM and i make 7 intervals lets say 1st interval 10:40AM, 2nd at 10:42AM, etc

You will not get the time of day. Check the start time for the activity and then add the time for when an interval started. 

Well, time of day is saved, but not displayed, you can check the raw file with laps.

Open the DevTools: F12 → Network tab, then open an activity's page, it lists all loaded files.

Search for splits, select it and check Response, each lap has startTimeGMT.