During busy debates, the Speaker may impose a formal time limit on backbench speeches to give as many MPs as possible the chance to speak. The Speaker can alter the limit during the debate if it’s necessary to accommodate more MPs.
If the Speaker imposes a formal time limit, the annunciators (the monitors around the parliamentary estate) will display the time limit and the clocks in the Chamber will show exactly how much time you have remaining when you’re speaking. You will be granted extra time of one minute for each of the first two interventions you take, which will be added to the remaining time displayed on the annunciator. If you take more than two interventions, you don’t get any more time.
If the Speaker hasn’t set a formal time limit, you should still bear in mind the number of other MPs who want to speak.