yep, so what I would do is

(rf/reg-fx
  ::delayed-dispatch
  (fn [{:keys [event delay]}]
    (js/setTimeout #(rf/dispatch event) delay)))

(defn delayed-dispatch
  [{:keys [event delay] :as args}]
  [[::delayed-dispatch args]])

...

(defn your-http-fx
  [args]
  [[::http-effect args]]

...

(rf/reg-event-fx
  ::failed-call
  (fn [...]
    {:fx (delayed-dispatch [::make-call ...] ... delay ...)}))

(rf/reg-event-fx
  ::make-call
  (fn [{:keys [db]} [_ delay]]
    {:fx (your-http-fx ... :on-failure ::failed-call)}))

obviously very pseudocode

but this is a perfectly acceptable use of fx - waiting for a delay is something that can be considered an "outside subsystem"

just store the number of requests so far, current delay, whatever either in the app db or implicitly in the looping chain

thanks @U3JH98J4R!