How i show an new form when my timer stop

How i show an new form when my timer stop

At my solution i've 2 forms (form1 form2), and form1 checks automatically
if user exist and if exist, these same form call the form2 and when form2
appear form1 hide.
Happens that in form1 i have an timer called "clock" that allow me control
time and when 15 seconds occours can call the form2 or show throught an
label that user does not exist.
At start my solution open 2 forms at same time, but i want that clock
running the 15 seconds and when clock.stop() method occours, solution
should be present form2 and hide form1.
Code:
private void Form1_Load(object sender, EventArgs e)
{
clock.Start();
//Checkuser
label8.Show();
editus uti = new editus();
Form2 formdois = new Form2();
uti.getxmlfile();
uti.check_node(formdois);
clock.Stop();
}
How i can do this?
Note: Do you understand my problem? (i'm portuguese and my english is a
little bad)