When requesting Hourly bars for NYSE equities we have noticed that the raw UTC time stamps have incorrectly been adjusted to account for Daylight Saving Time. The global metadata provides definitions for all existent time zones, which includes UTC offset, DST offset, and DST start and end dates, but only for the current year. NYC is defined as follows, with the UTC offset being -300 and DST offset being -240:

When we perform the time zone conversion for all the data records from UTC to exchange time to display in the chart, we use the relevant time zone definition to know when to use the DST offset and when not to. Hourly data goes back a year for NYSE equities so we get summarized data back to June of 2023. Because the DST definition does not account for last year the code is not able to adjust last year's data for DST.

Here is a concrete example...

The NYSE trades from 0930 to 1602 local time, so every trading day there are 8 hourly bars stamped (start-of-period) 0900, 1000, 1100, 1200, 1300, 1400, 1500, 1600. The data we receive from the Summaries API is stamped with UTC times and, when DST is in effect (records between 3/10/2024 and 11/3/2024), should be stamped +240, or: 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000. So far so good. Prior to 3/10/2024 the UTC bars we receive should be stamped +300, or 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100. Also good. The problem is when the data crosses into last year's DST prior to 11/5/2023 it is adjusted back to the DST offset, so we're getting 1300-2000. When we convert to local time we don't know about last year's DST definition so we adjust using the normal offset of -300 and the time stamps are all off by an hour.

UTC data that we receive should only be adjusted for DST for the current year as defined by the global metadata time zone definition. Hourly data prior to the current year's DST should not be adjusted for DST. This is how we receive it from TSI in Eikon.