What is the diffrence between two code snippetts

I am trying to create a splash screen form. Its opacity value set to zero. And I have a timer named tmrfadein. Its interval is equal to 5. If I use this code below then it works as expected, the splash form appears gradually.

if (Opacity == 1)
{
    tmrfadein.Enabled = false;
}
Opacity += 0.01;

If I use this code .Splash screen appears without waiting

do
{
    Opacity += 0.01;
}
while (Opacity <1);
tmrfadein.Enabled = false;

When I debug the code everything looks ok. What is wrong with second one