Cannot comment on your examples as they appear unnatural to me.
However, I would suggest you use
1. It's been about 3 hours since I came
2. I have been waiting for about 3 hours
Note: 'it's been' is a contraction for 'it has been' NOT 'it is been'
Disclaimer: Not a teacher or native speaker, been living in the US for 2 years.
Just for my curiosity, where did you get these examples from?
Student or Learner