Someone for whatever reason was not able to eat Erev Tisha B'Av. It came shkia (sunset) and finally he was able to find time or the ability to eat. Is it better for him to eat then during Bein Hashmoshos and be able to fast then all of Tisha B'Av. Or better not to eat during Bein Hashmoshos and wait until the he gets into a situation where he feels he must eat even if it's on Tisha B'Av itself?
Essentially the question comes down to, is it better to do a "sofek issur" or a "v'dei issur in a situation of an ones"?