'A' tells 'B' the results of an investigation he started at ten in the morning.
1-You have found all this out since ten o'clock this morning?
2-You found all this out since ten o'clock this morning?
Which of the two sentences '1' and '2' are acceptable here?
You could use either, depending on other factors.
One factor might be that if A had finished his research, the simple past would be used, whereas if the investigation is ongoing, 1 might be better.