Towards the end of the day generally, from like 22:00 or so. I think because the days ending and, most of the time, I've done nothing all day so feel utterly useless. Interestingly, this can also provoke me into being most productive at this time. But not always. I suspect that I'm also mentally tired by this time and this gives me darker thoughts than usual and I'm extremely panicked and stressed often during this period.
Luckily, it's also nearly bed time so I just go to bed and wake up reset most of the time.