The GridDateTimeColumn is using picker controls to select date and they are bound to a DateTime object. Because of this you are seeing the error when trying to filter column bound to a TimeSpan.
If you would like to have a column that displays hours you could use couple of approaches. If you would like to keep the GridDateTimeColumn you could bind it to a DateTime object and display only the time part from it.
Note that you would need to handle the filtering manually. You could use an approach similar to the one described in this article
Another approach you could use is to replace the column with a GridTemplateColumn or GridBoundColumn.
I hope this helps.
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