Oui plus vite que l'éclair !
En revanche, je me pose deux questions:
--- pourquoi le baseline-skip à 0.5 ?
--- pourquoi le default style ?
\version "2.21.0"
#(define-public (format-time-sig-note grob)
(let* ((frac (ly:grob-property grob 'fraction))
(num (if (pair? frac) (car frac) 4))
(den (if (pair? frac) (cdr frac) 2))
(dur (ly:intlog2 den))
(m (markup ;#:override '(baseline-skip . 0.5)
#:override '(baseline-skip . 0)
#:center-column
(#:number (number->string num)
;#:override '(style . default)
#:note (ly:make-duration dur)
DOWN))))
(grob-interpret-markup grob m)))
\new Staff {
\override Staff.TimeSignature.stencil = #format-time-sig-note
\time 3/8
\relative c'' { c8 c c }
}