I'm just getting into using effort properties myself and stumbled on your question. Here is a function modified from
org-fast-todo-selection which maps the index of the effort value to that number key (e.q. 0 -> 0:05 and 1 -> 0:15 per your provided EFFORT_ALL property).
(defun org-fast-effort-selection ()
"Modification of `org-fast-todo-selection' for use with org-set-effert. Select an effort value with single keys.
Returns the new effort value, or nil if no state change should occur.
Motivated by https://emacs.stackexchange.com/questions/59424/org-set-effort-fast-effort-selection"
;; Format effort values into an alist keyed by index
(let* ((fulltable (seq-map-indexed (lambda (e i) (cons (car e) (string-to-char (int-to-string i))))
(org-property-get-allowed-values nil org-effort-property t)))
(maxlen (apply 'max (mapcar
(if (stringp (car x)) (string-width (car x)) 0))
(expert (equal org-use-fast-todo-selection 'expert))
(fwidth (+ maxlen 3 1 3))
(ncol (/ (- (window-width) 4) fwidth))
tg cnt e c tbl subtable)
(set-buffer (get-buffer-create " *Org effort"))
(set-window-buffer (split-window-vertically) (get-buffer-create " *Org effort*"))
(org-switch-to-buffer-other-window " *Org effort*"))
(setq tbl fulltable cnt 0)
(while (setq e (pop tbl))
(setq tg (car e)
c (cdr e))
(print (char-to-string c))
(when (and (= cnt 0))
(insert " "))
(setq prompt (concat prompt "[" (char-to-string c) "] " tg " "))
(insert "[" c "] " tg (make-string
(- fwidth 4 (length tg)) ?\ ))
(when (and (= (setq cnt (1+ cnt)) ncol)
;; Avoid lines with just a closing delimiter.
(not (equal (car tbl) '(:endgroup))))
(setq cnt 0)))
(unless expert (org-fit-window-to-buffer))
(message (concat "[1-9..]:Set [SPC]:clear"
(if expert (concat "\n" prompt) "")))
(setq c (let ((inhibit-quit t)) (read-char-exclusive)))
(setq subtable (nreverse subtable))
((or (= c ?\C-g)
(and (= c ?q) (not (rassoc c fulltable))))
(setq quit-flag t))
((= c ?\ ) nil)
((setq e (or (rassoc c subtable) (rassoc c fulltable))
tg (car e))
(t (setq quit-flag t)))))))
org-set-effort and binding to a key:
(kbd "C-M-e") (lambda () (interactive) (org-set-effort nil (org-fast-set-effort))))
A possibly less intrusive solution is to add a case to
org-set-effort where, if
org-use-fast-todo-selection is set to
org-fast-effort-selection as defined above.
The advantages are that you won't have to bind it to a specific key, and it will also work with
org-agenda-set-effort out of the box.
I made a commit in my fork of org-mode showing how this can be done. After I use it a bit to make sure there's no edge cases that are being missed, I may submit it to the org-mode maintainers.