Grammaticality – Should I Use I Am/Have or I Graduated?

They are disappointing.

This is present tense and refers to "now".

I've been following the band for three years and they have been disappointing in their last five concerts.

This refers to a period of time in the past that may extend up to the immediate present. If I remember correctly, it is present perfect.

I've been following the band since they started playing and they were disappointing for the first few months.

This is past tense and refers to a point or period in time in the past, but not extending to the present. The event is in the past.

If the person is still in the place referred to as there, then the question How many days have you been there? (present perfect) is the only grammatically correct choice.

If the person is no longer there, then the question must be How many days were you there? (past simple).

Note: how many is sufficient; it doesn't need to be for how many.