This is a link to the post Venchka mentions:
https://whiteblaze.net/forum/showthr...ons?highlight=
Venchka's memory of the start dates with highest completion percentages is a little off. It's March 21 to April 7 that have the highest completion percentages. Furthermore, in another article I find that male/female completing couples keeping a journal at trailjournals.com take an average of around 180 days to complete. If engine and Caboose turned out to be "average" completers then starting in late April or around May 1 would be a bad idea -- it wouldn't leave them enough time.