There's a lot of values here with barely any explanation:

  [Thu 21:50:58 INFO ] Tile Render Statistics:
  [Thu 21:50:58 INFO ]   world.ct: processed=3025, rendered=3025, updated=1559, transparent=192
  [Thu 21:50:58 INFO ]   world.flat: processed=2641, rendered=2641, updated=1225, transparent=33
  [Thu 21:50:58 INFO ]   world.t: processed=97431, rendered=97431, updated=64363, transparent=29831
  [Thu 21:50:58 INFO ]   world_nether.flat: processed=1418, rendered=1418, updated=886, transparent=122
  [Thu 21:50:58 INFO ]   world_nether.nt: processed=12552, rendered=12552, updated=10194, transparent=3135
  [Thu 21:50:58 INFO ]   TOTALS: processed=117067, rendered=117067, updated=78227, transparent=33313
  [Thu 21:50:58 INFO ]   Triggered update queue size: 0 + 0
  [Thu 21:50:58 INFO ]   Active render jobs: world 
  [Thu 21:50:58 INFO ] Chunk Loading Statistics:
  [Thu 21:50:58 INFO ]   Cache hit rate: 60.11%
  [Thu 21:50:58 INFO ]   Chunks processed: Cached: count=7314212, 0.00 msec/chunk
  [Thu 21:50:58 INFO ]   Chunks processed: Already Loaded: count=80550, 178.69 msec/chunk
  [Thu 21:50:58 INFO ]   Chunks processed: Load Required: count=320632, 3.77 msec/chunk
  [Thu 21:50:58 INFO ]   Chunks processed: Not Generated: count=2066052, 0.00 msec/chunk

I'm trying to predict how much longer is left in a render job that's been running for days. There's no documentation anywhere as to what any of these numbers mean and I'd like to know about each.

not possible to predict as your system is finding chunks slower than it is rendering them, either increase the render speeds (fastrender sequence) or wait:
renderaccelerateinterval: .001

tiles-rendered-at-once: 10

maxchunkspertick: 400

parallelrendercnt: 10

fullrenderplayerlimit: 0

per-tick-time-limit: 200

fullrender-min-tps: 5
(configuration.txt) here the server has 10 cores, change the parallelrenderct to the amount of cores you have. Next do /dynmap pause all, restart and finally do /dynmap pause none.

the render stats are mostly self-explanatory, the queue size consists of the chunks that are being worked on, and the ones that are in the queue, the cache hit rate is as far as I know, how much percentage of the called chunks to render is already cached, but not sure.

@JurgenKuyper What about processed/rendered/updated?

Also, how large is a tile (in blocks) normally?

@JurgenKuyper What about processed/rendered/updated?

Also, how large is a tile (in blocks) normally?

I don't know, but guess they are the amnt of tiles that apply to that state

@thetayloredman a tile is a chunk normally in size, zooms and stitching can change that