The best answer to this is based upon how people read and how brains work in general.
Example of How Brainz Work
If u cn rd ths ur 2 cloz
Do Everything Possible To Keep Readers Reading
Sure, you can read that, but for some ppl* it will take longer. Even if it is a negligible amount of time measured you don't want it to take longer when people are reading your fiction. If it takes them too long they will quit.
*A little hidden joke in this explanation. :) Also, did you notice how the asterisk made you slow your reading for even a millisecond? That's the experience that writing number symbols can have on readers.
Writing Reading Conventions, Not Rules
Think about the reader, not about your writing.
The answer that you've been waiting for is:
Write out the number as a word. Why?
Because when a brain is reading words, it (generally) slows the brain down to switch modes and turn number symbols into words which are then added to the understanding of the sentence.
Jerry went fishing on Lake Timonga every 32 minutes he pulled in 3
Jerry went fishing on Lake Timonga every thirty-two minutes he pulled
in three fish.
Last Sentence is "Easier" (Faster)
I am a very fast reader, but if I read a sentence like the first I often stop for just a moment and read the first number as three two, then my eyes scan over it and re-read it as thirty-two. With the words, my eyes just keep flying over the sentence.
Something to consider.