How to increase ToolTip display time?

<Button x:Name="btnHelp" ToolTip="For new paragraph : press Enter &#x0a;For new line : press Shift+Enter">
 <ToolTipService.ShowDuration>15000</ToolTipService.ShowDuration>
</Button>

You need to use the ToolTipService and specifically the ShowDuration attached property.

You should be able to do the following after you set the tooltip:

ToolTipService.ShowDuration(e.Row, 10000)

Set the ToolTipService.ShowDuration property.