When using TrdSubTyp=“43” for Trade at Marker, is there a related tag which can be enumerated (custom?) to indicate possible marker times?
The appropriate tag for setting a pricing time is StrikeTime(443).
FIX does not provide a tag with enumerations to define the marker. StrikeTime(443) is a UTCTimestamp and not part of the trade messages. If you look at EP107 (https://www.fixtrading.org/extension-packs/) you will find that TAM goes back to ICE seeking coverage for “Trade at Morning Marker”, i.e. it is not about a specific point in time but about a specific price being issued and taken as reference. See also 41=Trade at Settlement Price. You could use TradingSessionID(336) to identify a time of day related to the TAM price. It is a field that has Reserved100Plus, i.e. you are allowed to define your own values as of 100.