The only really busy times are the weekends.
Weekday mornings I would guess.
Early mornings and during the day through the week. It's almost always busy on the weekends. There are no set times for off-peak hours though, so it will be what it will be. Your best bet would be to go and experience it for yourself a few times, then decide what's right for you. Also, beware that the second and fourth Wednesday of every month, the dog park is closed until 12 noon for maintenance.
On a hotter day, very few people / dogs are there mid afternoon 2pm - 5pm
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