How to make an animated set of images with a working duration per image

I want to make an animated set of images in python. I can't use an animated gif as I need more than 256 colors. I have tried an animated png but it seems the duration argument doesn't work. Here is a MWE:

import seaborn as sns
import io
import matplotlib.pyplot as plt
import scipy
import math
import numpy as np
import imageio

vmin = 0
vmax = 0.4
images = []
for i in range(3):
    mu = 0
    variance = i+0.1
    sigma = math.sqrt(variance)
    x = np.linspace(mu - 3*sigma, mu + 3*sigma, 100)
    row = scipy.stats.norm.pdf(x, mu, sigma)
    matrix = []
    for _ in range(100):
        matrix.append(row)
    cmap = "viridis"
    hmap = sns.heatmap(matrix, vmin=vmin, vmax=vmax, cmap=cmap)
    hmap.set_xticklabels([*range(0, 100, 4)])
    cbar = hmap.collections[0].colorbar
    cbar.set_label("Colorbar Label", labelpad=10)  # Set the label and adjust the spacing using labelpad
    plt.savefig(f"image_{i}.png", format='png')

    plt.close()
    images.append(imageio.v3.imread(f"image_{i}.png"))
    
imageio.mimwrite("out.png", images, duration=4)

Is there way to set the duration, or alternatively, is there another way to make an animated set of images that doesn't require any external tools other than python?

You are setting the duration:

imageio.mimwrite("out.png", images, duration=4)

Per the Pillow docs, duration is expressed in milliseconds. Setting duration=1000 results in a slower APNG.