29 January 1967
There was no studio session on this day but The Beatles were still working on "A Day In The Life"
This date is speculative. I first saw this photo on the internet circa 2008. The source captioned it, "The Beatles watch The Jimi Hendrix Experience at their manager Brian Epstein's Saville Theatre in London's West End".
This photo definently fits within the Pepper era. Reports have just John and Paul attending the show on this date. On 11 January (Paul) and 13 January (Paul and Ringo) attended two Hendrix shows at The Bag O'Nails. Perhaps, by this date, Paul and Ringo had convinced the others to attend this show. However, reports also mention all four Beatles attending a Cream concert on 5 February and a Donovan concert on 24 April. Both at The Saville Theatre.