Water as needed. Depending on the time of year, humidity, wind, location, and media, the pot will dry out at different rates. Check the soil with a chopstick or your finger, if it is still moist, it can wait awhile longer.
Bonsai media is usually more like different sizes of gravel and does not usually contain a lot of water holding materials. With a dry mix and a bonsai outdoors, you can easily have to water it daily, but it will still depend on how fast it dries out.
Bonsai are deliberately stunted and will eventually become pot bound. they need to be fed, pruned and repotted regularly. Usually the pot is only large enough to accommodate the roots so there isn't that much media in it.
It is good you can keep it outside year round, it will be better off that way in full sun.
This might help with basic juniper care.