When x-values are not passed, it takes numeric values 0,1,2,3,… In case of numeric axis, intervalType will be number. To set 12 hours interval, you will have to use date-time axis with interval: 12, intervalType:"hours". Else if you like to go with numeric-data, you can set the interval: 12 if it’s hourly data.
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Vishwas R
Team CanvasJS