At least the ESP-LLR challenge lasts mere 7 days, instead of 65 days as somebody suggested.I was just looking at next year's challenge series. No race is shorter than 5 days.
Some links:
old thread - Suggestions for challenges 2019
recent thread - 2019 Challenge Voting
tentative schedule - challenge/2019_challenge.php
recent thread - 2019 Challenge Voting
tentative schedule - challenge/2019_challenge.php