X-values can either be number or valid date-time object. In your case, its not valid date-object. Changing x: date[i], to x: new Date(date[i]), and passing date-time in one of the valid formats should work fine in this case.
Also, please take a look at this documentation page for information on rendering chart with date-time axis.
Still, if you are facing any issue or have other requirements please create a jsfiddle reproducing the issue you are facing so that we can understand your requirement better and help you out.
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Indranil Deo
Team CanvasJS