Unacceptable!
(Just kidding) Rootwork on junipers is best in early spring/late winter after risk of hard freeze is past (or if you can provide some protection). I say this because your tree is in a plastic planter and the surface of the soil looks broken down with very little void space in the soil. It is very easy to kill a juniper by keeping the rootball too wet in a plastic pot. If you haven't done so, make sure the tree isn't rootbound, and that the roots are healthy. Healthy roots + good soil means a strong tree and you will be able to do more aggressive work on it than you might otherwise do - and the tree will respond more strongly. At the minimum I would be prioritizing a repot in six months...
Additionally, be careful with junipers that you don't remove too much foliage in one shot. It is better to be cautious and remove no more than 50% in one session, and see how the tree recovers, before you continue to work the tree. If you remove too much in one session, you can get die-back on branches, or the tree may crash and die even when it is otherwise healthy.
This is the perfect time of year (beginning of summer) to prune junipers, since the tree should be at peak strength and have plenty of time to recover prior to the arrival of colder weather next fall. I would recommend creating jins on any big cuts - since you can always reduce them later, but you can't make them longer

Note that the harder you prune your tree, the more immature needle foliage you are likely to get. With time, as the foliage matures, you can coax it towards more mature / scale foliage by slowly reducing the immature foliage when it is located where you don't want it. Slower development and pruning will yield more mature foliage whereas aggressive work on the tree may result in more back-budding and development of interior branching, but that young/new growth may all be needle.