Conversation so far:
is michigan in the same time zone as new york
Michigan is the same time as New York.
what time zone are Michigan and New York in
New York and Michigan except for the four Upper Peninsula counties are located entirely within the Eastern Time Zone.
how many states are in the Eastern Time Zone
22 states and Washington D.C. are partially or fully located within the Eastern Time Zone.

Question: when did the regions come into effect
Self-contained rewrite: when did time zones in the United States come into effect