The timer is not for getting the current time. It is for triggering actions at a given time (or at given intervals again and again). If I read your question correctly, you don't need the timer.
If you want to set the
DateTimePicker to the time the button was pressed, set its
Value property:
void button1_Click(object sender, EventArgs e)
{
dateTimePicker1.Value = DateTime.Now;
}