Posting on here and Webtoons, I don't know? I would look at your stats. Look at hourly and daily to see when people are reading your comic. But you should also share through other outlets on different days at different times. But as a general rule: Post between 1:00 pm - 5:00 pm.* From a logical perspective, that when people start to get bored at work so it's the best time for a comic distraction. lol. As far as days, don't break convention. Wednesdays and Fridays are probably best.
Here's a good article on it:
*However, you should always check your own numbers because it may not necessarily be when YOUR readers are looking at your comic.
Another good and common strategy is to post early in the morning, but share on social media afternoon. You can use https://ifttt.com/ and Hootsuite to help manage this.
Also make sure your SEO is current and effective. And Due to the "pay to play" shift social media has taken, don't be afraid to put a little bit of money into advertising. Even a dollar a day will help your metrics and organic reach. Good luck.