A.P.
I don't think there's a definite answer here. Sorry. I can tell you how it was with me:
I nursed my first until he was 11 months old, and got pregnant the following month with my 2nd. I was 33.
I got pregnant with the 3rd only 2 months after stopping nursing the 2nd. I was 34.
With the 3rd, I got my period the day I stopped nursing completely (13 months after she was born).
With the first 2, my period returned sooner - I think I was doing what you're doing (twice a day).
Good luck!