At minimum how far apart should AM and PM runs be?

I would think 5 hours.

It doesn't matter at all as long as you get the miles in.

depends.

is the AM run a shake-out run to get the legs moving for the PM's track workout?

Are you doing an AM medium long run followed by a PM recovery run?

Is this just simply general aerobic miles during base phase?

^all of these scenarios change the answer.

I've gone out around 10 AM then have to go for my second run of the day earlier than usual and I went out at 4PM.

Had this happen many times. It's been an easy day though, an hour each time.

You would need to finish your AM run by 11:59.

And start your PM run after 12:01.

Natch.

six hours

4-6 hours, the longer the better but after 5 hours it doesn't matter much

Minimum 2-2.5 hours. I am not joking.

You can do them both in the morning if you want. It depends what you're trying to accomplish. The closer together they are the more recovery you can get before your next run, so if you're doing a hard workout you can do it within an hour or two of your first run and then have around 20 - 22 hours off before your next run.

The answer is 4 beers, unless the morning run is really light - you can then run only 3 beers late.r

12 hours.

six hours forty seven minutes. Anything less and you have ruined a day of training.

I often used to do a "morning" run at lunch and then run my 2nd run of the day at around 6pm. I averaged around 95-100 miles/week and would agree 5 hours was enough. Often felt much better on the 2nd run of the day/workout than in the morning. I felt the extra sleep was more beneficial for me.