Попробуйте добавить обновление холста canvas.update()
from tkinter import *
import time
root = Tk()
canvas = Canvas(root,width=1000,height=500)
x=0
y=0
canvas.create_oval(x,y,x+10,y+10)
canvas.pack()
start_time = time.time()
sec = 10
while (time.time()-start_time) <= sec:
canvas.delete('all')
x=20*(time.time()-start_time)
y=30*(time.time()-start_time)
canvas.create_oval(x,y,x+10,y+10)
canvas.update()
root.mainloop()