If you have individual request logs with timing infomation, you could construct that afterwards. It does take some effort to have an effective way of displaying these metrics. Where would you put an individual request that took 532ms and started at t=34.682s? Would you align all requests that started in the 34th second at t=34s, or look at completion time (ie within t=35s)?

Would you rather see "number of requests started at this ms" (you seem to suggest this), or is something else more interesting?

I think a sort of Gantt chart that plots duration of requests as well as starting time within the time span (e.g. a second or more) might be very informative. Each individual request on a different position on the Y axis, time on the X axis. Perhaps you have some bound on requests in flight, that could be the height of the Y axis, so you can easily see calm or busy periods.

At least our observability stack doesn't show this level of detail, but it would be very interesting to have it. (We do have calculated heatmaps based on maximum request time in Grafana, which is at least better than plots of average request times)