wpf tooltip on mouseover and mouseout

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

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.