Please explain the difference
1) I Hadn't been doing the Task since 29th April 2) I haven't been doing the task since 29th April
As I understand an exact time cannot be used with Present Perfect?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
An exact date can be used with Present perfect:
I have been working here since May 15th.
I can't think of a context where I would use either of your sentences, so I'll try and explain the difference between both verbal structures. This is tense sequencing:
I have been doing this for 3 hours, I'm exhausted.
I had been doing this for 3 hours when my mom walked in.
In the first case, we're in the present: the speaker has started doing something 3 hours ago, and is still doing it. Hence, he's exhausted.
In the second case, we're telling a story in the past: the speaker had started to do something a few hours earlier, then his mom walked in.
What did you want to say in your sentence exactly ?
The only context where I can see your second sentence is in a discussion such as:
Have you been doing this task since April 28th ?
No, I haven't been doing this task since April 28th, I have only been doing it since May 03rd.
But it is still very weird.