wpf tooltip on mouseover and mouseout

Your question isn't completely clear, and I'm not sure what you're looking for, but the things that will affect ToolTip duration follow:

ToolTipService.InitialShowDelay - Length of time in milliseconds between hovering over a control and when the tooltip appears. 0 = instant.

ToolTipService.ShowDuration - Length of time in milliseconds a tooltip will hang around while the mouse is over it. Setting it really high will be effectively a "never turn off" option, but there isn't a true always option.

ToolTipService.BetweenShowDelay - Once a tooltip pops up, this is the amount of time that must pass before InitialShowDelay is again observed.

Example:

<TextBox ToolTipService.InitialShowDelay="5000" ToolTipService.ShowDuration="2000" ToolTipService.BetweenShowDelay="10000" ToolTip="This is a tool tip." />

With this, when you hover over the TextBox, a tooltip will show up after five seconds. It will hang around for two seconds. And until you haven't looked at a tooltip for 10 seconds, there will be no delay between hover and pop-up.

If you just set ToolTip="Message". Your message will be shown only when the mouse is on the control.