I do not know how would it be correctly to use the Modal Verb Must in the meaning of supposition in the Present Perfect Progressive?
For example: 1) He must be sitting there already two hours. 2) He must have been sitting there alredy two hours.
The Present Perfect Progressive expresses that the action began before the moment of speaking but it's still in progress.
3) Is it correct to say alredy for two hours?
Please could you point out other my mistakes if i did in the questuion?