How long can I wear my regular tampons on my 2 and 3 day of periods?

I would like you to tell you that you can surely change it during break time. Moreover, it would be great if you change these more frequently. As you stated that you face a really heavy flow, then I would recommend you that you must change it every two hours. Even if the flow is light, don’t make a blunder by not changing for longer than 8 hours. It is fact that even with a pad, you have some lee-way, because even if you leak a little you'll be safe. It Is recommended that you must change it during one of your classes in the morning, then again at lunch. Moreover, the leakage depends from person to person. So, you can experiment it on weekends to see how long before you leak. Use a wide and more secure pad on the heavy flow days, this would be great to keep you on the safer side. Take care, and always carry an extra pad with you during the periods.