Answer: The inch a week is just a rule of thumb. Actually the watering time will depend on your soil and how far/fast the water penetrates. It will probably take quite a long time, depending too on your water pressure. You want to water slowly enough that there is no runoff, just the water soaking in. For a newly planted tree, you need to keep the soil moist but not soaking wet and you should monitor the soil moisture up until the ground freezes.
When you water, the water should soak down deep to encourage deep rooting. This can take a lot of water or a long time, depending on your water pressure and the type of soil (eg sandy or clay based) you have. You would water again when the top inch or two of the soil has dried. To see if you need to water, dig down a few inches and examine the soil.
If you use several inches of organic mulch spread over the root zone (but not touching the trunk), you will need to water less often. Keeping the soaker hose under the mulch protects it and helps it last longer.
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