Yorkie excersise...guidance?

how long per day should we walk our almost 4 month dated yorkie?
we usually take him 3 or 4 times a day probably 15 minutes respectively on a weekday.

on a weekend we do about 45 mins an hour around the woods and fields

what would you reccomend?
Answers:    i happen to know that 30 mins twice day by day is good exercise for such a hyper breed . the yorkie is a high energy breed .
I would muse that is plenty of exercise. I do walk mine everyday but mostly she runs and plays in the patio and gets her exercise there. Here is a site with lots of information on yorkies.
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