Chart vs Hour Lumps data on Date

I've had this problem over and over and I wonder if anyone can help.

The problem is mainly with getting Excel to realize that a date is a date (or a timestamp is a timestamp).

In the attached chart, notice that the data is charted incorrectly -- all the values for each date, regardless of hour, get lumped at one hour.

Sometimes I've been able to fix this by changing the date-time entry to a serial number, then simply formatting the x-axis to show it as a date.

That is infuriating enough.

This time nothing seems to help.

Is there a way I can get dates to chart as dates consistently?

Many thanks.