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The reason your decimalTimeToHours method is getting called so many times relates to how Angular change detection works. Angular keeps track of any bindings in the HTML template, and updates the browser dom when the underlying value changes. But, this isn't a magical process. In order to know when an underlying value changes, Angular has to manually keep checking if these values have changed. It takes the current value and compares it against the last value it saw for that binding. If the value changes, it updates the dom. The finer details of how and when this detection process runs is a huge topic. The important part, though, is that when change detection runs (which appears to be happening 6 times) it goes to your binding to get the current value.

The problem stems from your use of a function there right in the template. Each time change detection wants to evaluate the value, it has to call that function in order to determine the value (which creates a new string each time), and then compares that against the old string. Not a huge problem, but it's something you could easily be avoiding. One solution would be to use an angular pipe to format the data the way you want to see it in the table: