@frankchapell
None of the RICs you mentioned in your question actually exist. But I'll try to answer your question in generic terms. KRW and TWD are liquid currencies and their indicative spot exchanges rates against USD contributed by banks are continuously updated 24/5 in RICs KRW= and TWD=. INR is a far less liquid currency, which is almost exclusively traded during Asia hours. The difference between spot exchange rate RICs ending with "=" and those ending with "=D1", "=D2", "=D3" and "=D4" is that the former provide indicative rates contributed by banks and the latter are derived from actual trades on Thomson Reuters dealing and matching systems. For more info on how these rates are derived see page DEALINFO in your Eikon application. You can also find the trades executed on EBS matching system in RICs XXX=EBS. D1/D2/D3 and EBS RICs are only available to subscribers of these systems. D4 RICs are available to everyone, although they may not be included in all Eikon variants. I don't think you'll find any significant difference in hours during which the rates update between any of these types of RICs.
Finally, this forum is intended for software developers using Thomson Reuters APIs. Your question is a pure content question not related to any specific APIs. If you need any further clarification on your question or if you have any other content search and explanation questions, the best resource to direct these questions to is Thomson Reuters Helpdesk, which you can access by either calling the Helpdesk number in your country or by using Contact Us capability in your Eikon application.