The Oxford English Dictionary defines to get it over with as
to complete an unpleasant or tedious but necessary task promptly.
The Oxford dictionary online (ODO) defines get something over with as
Do or undergo something unpleasant or difficult, so as to be rid of it.
So yes, one could say this to someone who is bent on talking and talking about some unpleasant chore and not really wanting to do it.
Examples from the OED:
The thing had to be done, and the sooner he got it over with the better.
(1899 Vassar Misc. (Vassar Coll., N.Y.) Feb. 211)
I sense that he is dog-tired and just wants to get the meeting over with.
(2004 S. Mehta Maximum City 332)
From the ODO:
‘I suppose it was a good idea to get it over with quickly.’
Once a task is finished, you can say the task is
over and done with or over with
It will be hard work to get through the three months to Cousin Maria's wedding; I wish it were ‘over and done with’.
(1822 M. Arden Diary in National Mag. (1856) Nov. 54/1)
I was shaking and sweating at the checkout, wanting it to be over with, wanting to be out of there.
(1999 T. Parsons Man & Boy (2000) xii. 101)
See also the ODO