What I would like to do is display the following in a form:
Open [15] minutes before class
Where [15] is a text-field. Is this possible?
Use a 'composite component' by adding the required parts to a JPanel. E.G.

import java.awt.FlowLayout;
import javax.swing.*;
class TimeBeforeClass {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JPanel gui = new JPanel(new FlowLayout(FlowLayout.LEFT, 3,3));
gui.add(new JLabel("Open"));
gui.add(new JSpinner(new SpinnerNumberModel(15,0,20,1)));
gui.add(new JLabel("minutes before class"));
JOptionPane.showMessageDialog(null, gui);
}
});
}
}
Note that I swapped the 'textfield' for a JSpinner - a more suitable component for selecting 'time in minutes'.
Can I have a textfield inside a label?
answer is, yes you can, this is basic property of Java AWT / Swing Objects
JComboBox, JTable, JList, JSpinner, JFile(Color)Chooser.... are compound JComponents, you can extract all JComponent and put that together again.
you can put any of JComponents to the another
only JFrame/JDialog/JWindow and JPanel have got implemented LayoutManager by default in the API, for rest of then you have to implements proper LayoutManager
I think I have not understood. But, I'll try:
You can get the text from a TextField:
label.setText("Open " + textField.getText()+ " minutes before class");