When does the past happen? In the past, right? Well, that’s a circular definition. That doesn’t tell you anything. Let’s try again.
Try to see something from the past. Try to hear something from the past. Try to touch something from the past. When can you ever hear, see, or touch anything from the past? Whenever you hear things, see things, or touch things, the experience is always happening right now.
The past isn’t something that happened some time ago. The past is something you’re creating right now. Or, another way to say this is that you experience the past only as a memory (which you can experience only in the present).
There is no past, except what you remember of it right now. There would be no past without you here to consider it. The past happens right now, doesn’t it?