USE
We use Present Perfect Continuous
to talk about actions that started in the past and continue up to now (or just before now) .
They have been working in the garden since ten o'clock.
We want to emphasise the duration of an action. It does not matter whether it (action) has been finished or not.
NOTE!
We do NOT use Present Perfect Continuous with stative verbs and the verb 'be'.
We use Present Perfect Simple instead.
TIME EXPRESSIONS (or KEY WORDS)
since
They have been working on this project since June.
for
They have been working on this project for six months.
recently
They have been working on this project recently.
lately
They haven't been working on this project lately.
How long?
How long have they been working on this project?
all day (morning…)
They have been working on this project all day.
Revise when 'since' and 'for' should be used here.