I have been doing doubles for about a year now. Because of a hectic and strange schedule the past couple weeks, I have been running some of my runs only two hours apart. That got me thinking, what is the optimal rest between runs in a given day? What should be the minimum? Is there some minimum time between runs - 1 hour, 2 hours, three hours - at which point it just makes more sense (in terms of recovery or any other reason) to run a longer run instead of two shorter ones (say one 12 miler instead of an 8 and 4)?
Thanks for all the helpful replies.