What is the idiomatic way of saying 'stealing time', if someone is so busy and he wants to work on something by sneaking to it?
One can actually say "I managed to steal a few precious moments / minutes / hours with my family."
“To my delight, before the graduation ceremony began, I was able to steal a few minutes with an old friend.”
To "steal" time in this way is to be able to assign, set aside, or reserve that time for a particular reason or activity. The presumption is that there other demands for this time.
So "I was able to steal a few a few short hours away from my job to ..." (usually used in a past time-frame).
On the sly
on the sly
1 done secretly, especially because you know you should not be doing it
I’m supposed to be on a diet, but I still have the odd candy bar on the sly.
Macmillan : on the sly
And on the sly, she focused on the interesting stuff. She made her bones as a news and feature writer, editor, and translator, especially of literature. Font screams in her sleep, disturbed by eerie nightmares.
from the about the author section of Silvia font's Musings on the Dark.