Two thoughts...
Depends on how bad you want to kill a deer, and only you know for sure.
I have one field I started glassing about a month before season. Deer entered the feild at the same time every night, almost to the minute. I would do the half hour thing and setup on the trail, stick one and leave. It almost always was a 30 minute hunt.
Deer move all day and they will be in and out of fields all day for a number of reasons. If you really want to kill a deer you have two options. Stay all day or watch the field enough that you know exactly what the deer are doing.
Over the years I've probably killed more deer between 9:00 and 11:00 with more of them coming between 9:00 and 10:00. in the morning. I'm convenced the reason is that's when everyone else gets down and goes home. They bumb deer and many times don't even know it. You want to be on an exit trail durring those times.
As for evening times, I pattern the hunters. If everyone shows up at 3:30 pm to hunt then I want to be in my spot no later than 2:30 pm. That too makes for short hunts.
This works for public land and farm land that has hunters up to a mile away. I've also learn deer pattern hunters too.
If you're not sure about an area it's best to hunt until 11:00 AM and start up again at 2:30 pm. The will cover 80% of deer movement in high traffic areas. The bottomline is just make sure it's fun. If you hunt enough days you can hunt the same 30 minutes every day and a some point you'll kill a deer. If that's fun for you then do it. If your goal is to put meat in the freezer in the shortest amount of days then just hunt longer on the days you have available. You have the right to hunt as much or as little as you want.