The fix

import tkinter as tk
import tkinter.ttk as ttk

import time


class App(tk.Tk):
    def __init__(self):
        super().__init__()
        self.rowconfigure(990, weight=1)
        self.columnconfigure(0, weight=1)
        self.title('Timed Events Demo')
        self.geometry('420x200+20+20')

        var = tk.StringVar()

        tk_spn = tk.Spinbox(
            self,
            value=0,
            from_=0, to=1000,
            values=list(range(0, 1000))
        )
        tk_spn.grid(row=0, pady=5)

        ttk_spn = ttk.Spinbox(
            self,
            from_=0, to=1000,
            value=0,
            values=list(range(0, 1000))
        )
        ttk_spn.grid(row=1, pady=5)

        self.t1 = round(time.monotonic() * 1000)

        def do_work(e):
            wdg = e.widget
            old_val = wdg.get()

            def func():
                t2 = round(time.monotonic() * 1000)
                if t2 - self.t1 < 500:
                    e.widget.set(old_val)
                    return
                self.t1 = round(time.monotonic() * 1000)
            self.after(0, func)

        tk_spn.bind('<<Increment>>', do_work)
        tk_spn.bind('<<Decrement>>', do_work)

        ttk_spn.bind('<<Increment>>', do_work)
        ttk_spn.bind('<<Decrement>>', do_work)


def main():
    app = App()
    app.mainloop()


if __name__ == '__main__':
    main()