For night/day framerate issues, adjust start-times and set play-speed to zero.
The real time shadow rendering is very taxing on performance, particularly during Dusk/Dawn phases. Players with a wide variety of rigs, even very powerful hardware, report frame drops during these phases.
Proposal: Consider setting the play speed to zero (sun light does not move, remains fixed in the sky, constant), and adjusting the start times (exact lighting conditions) accordingly.
Community thread and StrawPoll is here: https://mwomercs.com/forums/topic/253467-poll-dynamic-time-of-day-removal-would-you-prefer-slightly-more-performance/
Player: CainenEX Suggest that PGI looks into baked lighting for the static objects, such as buildings. This will increase performance while keeping this feature in.
Otherwise revert to Taro's original suggestion.