Windows specific so moved to Window programming.
Your dialog should get a WM_PAINT/OnPaint message when it needs to be drawn - perhaps initiating your timed image there may be of some use.
If this is just intended as a 'splash screen' then you'd just generally show it and destroy/hide it once the time interval had elapsed. In this context, starting the display in OnInitDialog would be fine and terminating it in whatever timer you're using (eg WM_TIMER, SetTimer) would be sufficient.