Using the ray-tracing feature, it seems as though day and night have separate minimum light values (whether this parameter is set by the resource pack, I'm not sure.) In my case, the minimum light value for daylight (the moment just before the sun dips under the horizon) is much brighter than the minimum light value at night (the moment just after the sun dips below the horizon). This causes the lighting to change from bright to dark in an unnatural, instant way. (See video). As the Title/Summary states, I suspect there's some kind of re-calculation or transition to a separate ray tracing state/environment since the phenomenon can even be observed while underground or indoors (i.e. even light emitted from blocks is re-calculated).
On or off, the Upscaling (DLSS) feature does not affect the issue.

RTX Resource pack used in reference footage: Kelly's RTX Conversion
Issue persists in various different resource packs that are tied to maps downloaded from the Marketplace.

System Information
System type 64-bit operating system, x64-based processor
Processor: AMD Ryzen 5 3600X 6-Core Processor 3.80 GHz
Installed RAM: 32.0 GB
Graphics: Zotac AMP Holo RTX 3070; NVIDIA Driver v. 471.11
Storage: Samsung NVMe SSD 980 PRO 2TB