Square: do you have to do all reps at once?

[NinRick]

I had to chant the mantra 36 times.
Did 23, got disturbed, and did the remaining 13 2h later. Does the square still work?

 

[Hp. Hoodedcobra666]

It should be done in one sitting, that would be better.

 

[lilquote]

It should be done in one sitting, that would be better.

I have been told that it wouldn't ruin the working to take a small break like halfway through the number of vibrations. Is that true?
I remember, doing the mercury square, the energy was really intense for me and I had to take a couple of minutes to breathe every now and then. I ended up ruining the working later on for a different reason but it's still something I've wondered about for next time.