How much difference is there from one side of the world to the other? Does it vary with different world sizes?
Code looks something like this:
int32_t getLocalTime(int16_t region_x)
{
int32_t world_width = world->world_data->world_width;
if (gametype == DWARF_ARENA || gametype == ADVENTURER_ARENA)
return world->arena_settings->time;
else
return ( (region_x - world_width/2 + cur_year_tick%10 + cur_season_tick*10 + 1200) % 1200 )*2
}
So it looks like it differs by
(world_width - 1)*2 (in whatever unit it's returning) from one side of the world to the other (if my math is correct.)
Since the value ranges from 0 to 2398, I suspect each value is 1/100th of an hour. Therefore, for the available world widths:
Pocket (17): 0.32 hours
Smaller (33): 0.64 hours
Small (65): 1.28 hours
Medium (129): 2.56 hours
Large (257): 5.12 hours
The earth would be width 1200, or 4.67 times a large world width. I'll have to see if that lines up with what's known about DF world sizes.
(Edit: That's nearly 18 times larger than a large world is estimated by DF physics to be. I guess DF days might be 18 times shorter than ours.)
I know this is used in temperature calculations, at least. Someone will have to test in adventure mode if it affects the position of the sun.
Edit: Looks like it's checked in "Sleep until dawn", so the sun is definitely affected.