How long does it take for UEA to hand out offers or rejection?

Totally normal.

All competitive Unis make offers gradually and cautiously, and will make final offers right up to early May.
This ensures they hit their 'numbers' targets and are confident of filling courses but not over-shooting.

There will be thousands of people in the same situation at the moment so don't worry.
You still have a very good chance of an offer - hang on in there.