I think you are pretty close with what you are doing. There are a couple "rules of thumb". Some say 5 gallons of water per inch in caliper per week. You can figure your flow from the hose and see it you are hitting the mark. Another is 1" of water per week. Thats easy with a sprinkler and a coffee can. Flow water till you have an inch. One thing to remember too much water can be as detrimental to tree health as too little. Too much will drown the tree, too little can put the tree into a semi dormant state until water is available. The balancing act it getting it just right.