Offwindows in psychopy

Hi, internet!
My experiment is about Vep(Visual Evoked potential)
Can I first pre-draw my stimuli (many frames) on offwindows then just flip them?
Since I’m drawing all my stimuli on one window and keep flipping it, which is too time-consuming, so the time isn’t precise:

For example, my monitor’s refresh rate is 120Hz, so if I draw 240 frames, the processing should be done in just 2 sec, but now it takes like 3.8s, how can I cope with that?
Here’s part of my stimuli’s code:

for frame_i in range(240):
tic = time.time()
for ii in range(32):
toc = time.time()
print("%.5f" % (toc-tic))

I printed out time for drawing and flipping every frame,
Every time takes around 0.01s