@mpilarw7 for your particular case , enter 1 day as business day. This has been the case for ever ( that I can remember).
Generally, in order to meet the Physical Presence Test ( in a test period of 12 continuous months abroad, be away from USA for 330 days ), one needs to file a return after having met the Physical Presence Test. Else as you found out, one has to amend to take advantage of the Foreign Earned Income exclusion.
I am assuming here that your son is employed by a local entity or a wholly owned subsidiary of an international entity.
Is there more I can do for you ?
