How to take into account man hours in a Service Bulletin?
Elapsed time is the total man hours divided by the number of techs assigned to the task.  So 40 manhours will take one tech 40 hours to complete or 2 techs 20 hours.  If the number of techs to be assigned is up to the supervisor or a scheduler/planner, I would just include the total man hour estimate.  If the job card specifies the number of techs required for the job, then include the elapsed time based on that.

Note that on the first several aircraft modified under an SB, the actual man hours will exceed the SB estimate by a large margin, maybe 50% or more, until the technicians involved get through the learning curve of the task, and even then will probably never get to the SB labour estimate, which assumes perfect conditions and no wasted time.  If the OEM is giving a labour credit that can be charged back to the OEM at some hourly rate, it will be based on the SB estimated labour, which is derived from the proof installation of the SB, not the actual hours used.