Let's say time travel is possible, Time-Turner style. You are age 31. You travel back 20 years to when you are 11 years old, before your Bar Mitzvah. At that time period, you were not Chayav ...
The Mishna (Berakhot 4:1) brings the opinion of R' Yehuda to the effect that the latest time for shacharit is the fourth hour of the day. In explaining R' Yehuda's opinion, Kehati elaborates upon the ...