Something might suit 27th or 28th. Maybe even a lunchtime meet up at a pub in the Herts / Essex / Cambridgeshire borderlands?
I can recommend the Woodman at Nuthampstead. Other options available.
https://www.woodmannuthampstead.com/
I've been to the Woodman many years ago on a CTC ride - maybe we'd need to book, but sounds like a good plan for a social meet-up in addition to the perm?
For the group perm I'm suggesting a Boudicca's Revenge 100km, reversed. The advantage of this is there's the option of a gritted route for most of the first stage up to Haslingfield, via the B184 then the old A11 (B1383), then via Whittlesford to Newton and Harston. However the scenic route via Henham to Newport, then up into the hills from Littlebury, is much nicer.
Dunmow-Haslingfield 51km (scenic)/45km (minimum distance, B184 etc) elevenses at the Mohak café - need to check opening.
Haslingfield-Buntingford 26km lunch at The Bull pub/Buntingford Coffee shop - loads of other options, those are just favoured venues.
Buntingford-Dunmow 32km (minimum distance, preferred option via Furneux Pelham, Manuden, Elsenham and Great Easton is 35km).