Without knowing your specific Tesla model and exactly where you are planning to go at the Grand Canyon for this trip or what you are going to do driving wise when you get there.... You probably don't need to buy the CCS adapter for this trip.
Eh, like other posters in this thread have commented I think you're probably overly optimistic on that, but it is basically an aside to whether or not you should buy the adapter for this particular instance.
The big problem in this analysis is that the CCS version included 3 EA sites and the one you didn't bold is the one that matters big time here:
"Grand Canyon Visitor Center (Grand Canyon, AZ) [Electrify America]." That site is effectively the site that makes the difference in travel times between your two scenarios. The issue here is ABRP is erroneously missing the below supercharger for whatever reason. It isn't exactly new either as it has been there for 5 years.
There has been reports of a supercharger sighting in Tusayan (Grand Canyon Village), on the south side of The Grand Hotel. 8-10 stalls. No photos provided though - and it isn't on Tesla's planned map, so thought I would ask for additional confirmation here before adding to supercharge.info...
teslamotorsclub.com
Knowing that said supercharger is there and working
The Grand Hotel at the Grand Canyon (1) | Grand Canyon Village, AZ | EV Station is going to change your math quite a bit, because the majority (basically the entirety) of the time advantage that ABRP was giving the CCS adapter was solely based on the EA charger there versus ABRP not thinking Tesla had DC fast charging across the street. This is manually verifiable by creating a waypoint at the Tesla supercharger in ABRP and telling it you can charge up to 150 kW there.