You may not want to move them into a pond yet, but a 6 gallon tank is awfully small for 10 fry. If you increase their tank size, they will grow much faster and you will be able to move them to the pond sooner. Water volume is extremely important when it comes to fry growth.
Move them to the pond only when they are too large to fit into the adults' mouths. This may be anywhere from 4 months to 7 months old, depending on the individual care you've been giving them.
Also keep in mind that it is barely Spring, and you may only want to move them into the average pond when the pond temperature approaches the current fry tank temperature. Dropping them into a much colder pond can cause fry to stop growing, cause deformities, etc.