@dsrikanth Create calculated column for HOUR and MINUTES using dax as below. Then use scatter chart with x-axis as hour, y-axis as minutes, timestamp column as Details and observation column as Values.
@ankitpatira The user would need to go to Desktop to follow your suggestion - correct? Not knowing the data source I am just wondering if going to Desktop is possible or can one do your suggestion within Service?
@dsrikanth, why you don't want to show the aggregation value in the chart? If you want to show detailed data for every record, you have to choose the Table chart. Like @ankitpatira mentioned, you can create a hour slicer to filter second's records, then convert observation into different online color blocks images.