Depends on your routine. Deep work is the time when you’re not hungry, you’re not sleepy, you’re fed just enough, everyone around you is busy going about their stuff so they won’t interfere when you’re taking your space – it should be a time when you’re your most productive. For me it’s sometime between 2 and 6 pm – depends on the time I have my breakfast and lunch. That’s why it varies. Right after lunch, I feel sluggish so that’s not a good time. Maybe an hour or a couple of hours after lunch… or perhaps between 5 and 7 pm … assuming it’s a 10 am to 7 pm kind of working day.