I expect the answer to be - type in -0- to override.

Sch SE, part III, line 18 "Enter the portion of line 3 (SE profit) that can be attributed to March 27, 2020 through December 31, 2020.  The field is pink automatically.  Instead of asking IF the taxpayer wants to defer SE taxes I [assume] ALL of my clients will say NO to the deferral, that I should put in -0- and answer the question incorrectly (not that I really want to spend time trying to figure out 280 days worth of their profit anyways...)