Section 301.9100-2 allows a 6-month extension of the April 17, 2018 deadline for recharacterizations as long as you filed by April 17, 2018. If the recharacterization occurred before April 17, 2018, section 301.9100-2 doesn't really apply, but it probably wouldn't hurt to include it as long as you filed your 2017 tax return by April 17.
