my folder structure:

path/to/files
├── 01.m4b
├── 01.txt
├── 02.m4b
├── 02.txt
├── 03.m4b
└── 03.txt

I use this command:
subplz sync --device cuda --language en --overwrite-cache --stable-ts --word-timestamps --max-words-per-line 8 --max-line-width 40 --max-line-count 2 -d "path/to/files",
the output .srt are as same as the subplz sync --device cuda --language en --overwrite-cache --word-timestamps -d "path/to/files".

part of generated subtitle:

10
00:00:25,360 --> 00:00:26,360
the floors,

11
00:00:26,360 --> 00:00:27,572
the ceilings.

12
00:00:28,380 --> 00:00:33,980
Broad black smears crossed the blistered paints and gilt of once-bright murals,

13
00:00:33,980 --> 00:00:39,072
soot overlaying crumbling friezes of men and animals which seemed to have attempted to walk

14
00:00:39,072 --> 00:00:41,332
before the madness grew quiet.

I actually dont want lines too long as 12 and 13, I want to split it to around 3~6 words for one timestamp, could I make it using subplz?

And i dont know how it analyzes the .epub, when I use the whole book and separate chapter audios, every '.srt' is the whole book content. maybe it ask a strict '.epub' chapter style I guess. But the SyncCache/*.subs seem to be right. That's why I split the whole book into separate chapters (it contains more than 10 books of this series).