@Ahmed Imam Attia posted:
Is using the present perfect in the following sentence correct?
- I have finished since 12 o'clock.
No, that sentence is not correct, because the action of finishing is not durative. You can say, for example:
- I finished at 12 o'clock.
- I've been trying to finish since 12 o'clock.
"trying to finish" is something that can extend over time, from some point in the past till now, and that's why it works with "since."