I think you should be more concerned with getting a healthy puppy! The when will happen when the time is right.
I am going to elaborate on the health concerns of Yorkies and there are many! You want to investigate a breeder who health tests for these risks. And I guarantee you no-one will sell a puppy for $350 who actually does do all the health tests; they are pricey and will be factored into the cost of the puppy.
In relative order of frequency in the Yorkie
1. Luxating Patella or loose knees. The bane of most toy breeds!. Can be mild ie a grade one, or moderate to severe Grades 3/4. The higher grades usually require surgery. That cost alone is anywhere from $2000 to $4500 depending on the complexity of the repair required. /
All breeding pairs should have an LP evaluation and be free of LP. This will be shown on the health database
CHIC.ORG
2. Retained baby teeth. Usually will need to be surgically removed, often done at the time of neutering. This can/will increase the cost of the surgery. Prices vary a whole lot by vet.
3. Hip Dysplasia and or Leggs Perthes. Currently on the rise. An FHO surgery is again somewhere in the neighbourhood of LP surgery.
Breeding Pairs should have Xrays done and submitted to
Orthopedic Foundation for Animals for evaluation and be clear of hip disease.
4. Liver shunt and or Liver Disease. Quite prevalent in the breed. Extrahepatic shunts require surgery and again depending on the complexity surgery can range anywhere from $1500-$3000+ dollars.
5. PRA - Progressive Retinal Atrophy. Breeding pairs should be examined yearly by a Board certified opthamologist and be registered on the CERF data base.
cerf.org -
6. Hyperuricosuria and related Bladder Problems. ie Bladder Stones. This is the one DNA test available that breeders can see if their breeding stock is a carrier, clear, or affected.
7. Allergies/Skin Problems/Digestion problems. These are all variable. Many yorkies can be fussy eaters, have allergies to different things, and have gas etc.
8. CT or Collapsing Trachea. Neither breeding pair should suffer from this disease. evaluation by vet recommended.
As you can see from this list the concerns are many.