The party responsible for determining the limits for construction?

In Ballast practice exam question 144 : Who is the responsible party for determining construction time limits? Their answer is contractor and subcontractor. Why is subcontractor also included in this answer? I thought the Contractor is the only person submitting the schedule to the owner.

Also, who determines the substantial completion date? Why is it the Architect? Doesn’t  the contractor first notify the Architect? I think I am hung up on the words " Determine" , "Authorize", " Issue" ,... can someone please explain more?

Also, on another note, if before bidding, the lobby changes to be two floors instead of one floor,and the prices go up, and the owner doesn’t want to change the bid date, what would be the solution? should the architect include this in an alternate?

Thank you very much.