Choice between option A and B is more about how well the items/quantities can be defined and where the Employer wants the risk to sit. The works are re-measured, so the Contractor gets paid for the amount they do, and given the Employer produces the BofQ any errors/omissions in the B of Q will be a compensation event.
Option A it is down to the Contractor to produce the Activity Schedule and therefore any errors in quantities or omissions altogether will be Contractor risk. If as an Employer you issue an indicative activity schedule, this is fine, but you just need to emphasize that you want that filled in for tender comparison purposes, but they are free to add more detail as submit/reference in data part 2 as their activity schedule to be used to assess Price for Work Done to Date.
Option A it is down to the Contractor to produce the Activity Schedule and therefore any errors in quantities or omissions altogether will be Contractor risk. If as an Employer you issue an indicative activity schedule, this is fine, but you just need to emphasize that you want that filled in for tender comparison purposes, but they are free to add more detail as submit/reference in data part 2 as their activity schedule to be used to assess Price for Work Done to Date.