C# - Gridview Update Changing Update Parameter?

I have a Gridview where I can modify the Time portion of a DateTime field. The update method is working well, except for one thing:The field should only allow the time portion, e.g 08:23:09 but on the Database it saves it as a full DateTime, e.g 10/18/2010 08:23:09 AM. The problem is that upon editing, instead of adding the existing Date portion, it adds the current Date portion. So if I am editing the item from the last example into 08:25:09 instead of adding it as 10/18/2010 08:25:09 AM it adds it as 10/20/2010 08:25:09 AM which is obviously undesired behavior.Here's how I am doing the update:

protected void grvOutHour_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
GridView grvOutHour = (GridView)this.grvReport.Rows[grvReport.EditIndex].FindControl("grvOutHour");
TextBox txtBox = (TextBox) grvOutHour.Rows[e.RowIndex].FindControl("txtEditOutHour");

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