As a follow up from the content team, for Elektron collected venues we should be publishing times in GMT/UTC for all time-based fields. However for legacy venues still collected on IDN (but available on Elektron distribution) times can be in local time rather than a standard consistent time.
TRDTIM_1 has been allocated as a backwards compatible only field in our data models, which means that going forward for new venues we would use SALTIM_MS or SALTIM_NS for recording the transaction time of a trade (associated with TRDPRC_1) and not use this field at all (just a warning if you are considering using it that eventually this field will be phased out as more venues appear on Elektron and we start to remove older legacy fields).
In general, the timezone associated with FID TRDTIM_1 is GMT. I have put in a request to confirm this. If you are not looking at the raw feed but instead within an application such as Eikon, the TRDTIM_1 may be converted to the local time zone, depending on the personal settings.
As an aside, all market data APIs, such as RFA, EMA, ETA etc are data agnostic. The API will not manipulate or attempt to normalize the content that is coming from the ERT/Elektron servers. All data coming from the servers are left untouched.
All date, time and datetime fields in OMM are supposed to be in UTC. I believe this is a documented convention.
However, there's nothing which enforces this. You can potentially have a provider application who didn't get the memo, so to speak, and therefore doesn't comply with this convention. But as far as data from Thomson Reuters goes (meaning their Elektron feed or any of their direct feeds) you can certainly rely on this. So yes, on an Elektron feed, this will be consistent across exchanges because TR has "normalized" such fields before they are being published.