THE RULES

To talk about activities that are still continuing, ⋅ we use the present perfect continuous:

I’ve been working since 6.30.

To ask about duration, we use How long + present ⋅ perfect continuous:

How long have you been sitting here?

To talk about duration in negative sentences,

we ⋅ use the present perfect simple:

We haven’t used that room for years.

(not: We haven’t been using...)

To talk about the duration of the activity, we use:

… for +a time period (“for two hours”, “for a week”, “for a long time”, “for ages”)

… since + the starting point of the activity (“since two o’clock”, “since March”, “since this time last year”). “Since” means “from then until now”.