[dzdt]

This is a same problem in financial markets. Things like options contracts depend on a value observed say at 10am New York time on a particular date a decade in the future. If the daylight savings time schedule changes between now and then then the UTC time of the expiry of the options contract will change. The right reference isnt UTC or EST or EDT but "NY City local time" (or Tokyo or Warsaw or Mexico City or whatever is the relevant jurisidiction).