Day 1 – Berachos 2
We learn that the time for Shema ranges from the time poor people begin to eat until dawn. With the advent of electricity, poor people do not eat so early anymore.
However, it has become popular for the elderly to eat dinner early, between 4-5 PM, as they have less digestive enzymes, this helps decrease nighttime indigestion – as noted here
Can we rely on this early dinner time to allow the Shema to be recited as early as 4-5 PM?