Sylvia,
I have a female Boxer that has split heats. But she doesn't allow the male to breed on the firt heat. She has a discharge that lasts about 10 days but she doesn't swell much. And then about a month later she starts having the discharge again and swells. We breed her on days 9 & 11 and sometimes 13 of the second part of the cycle (if that makes sense). Since I know her and how her cycles work this works out for us.
I know she's not a Yorkie but I hope this helps anyway.
Carrie