[tex4ht] problem with slow compilation of large latex file with large math content

[Karl Berry]

    But I do not know how to decide if I need one run or two or three?

You need three runs if you are starting from scratch.
After the first time, in general, you only need one run unless you are
modifying the things that go into the cross-references (section names,
labels, bib entries, etc.).  

Ordinarily it's not worth thinking about, since the runs are fast
enough.  I only mention it here because if you're repeatedly doing three
five-hour runs when you only need to do one, that would clearly be
undesirable.

    I call make4ht to compile the file

I don't know anything about make4ht, that's Michal's bag ... Perhaps it
is already smart enough to avoid multiple runs when it's not necessary.
(I'm having deja vu, did we already discuss this, Michal?)  -k