I'm not sure there is a bad time to start something like that, honestly. I suppose it depends on how much work you're willing to/can put into it right now? And what you want to get out of it?
I don't have a discord for my story and don't know of many that do, but a friend of mine made one for her series and it's thriving. Her story is very popular over on Webtoon, and also a young adult series which I think lends itself to the right crowd for discord to begin with. She already had a big following that frankly needed somewhere else to go and be chatty/horny/whatever teens are doing these days. It looks like a hell of a lot of work though. I think she has three or four moderators wrangling denizens round the clock. There are events, contests, factions, emojis the whole shebang.
Here's a screeshot of some of the channels in her server to give you an idea of what could be:

Of course you don't have to make it that involved if you don't have the time. Loads of servers aren't. If all you desire is to give readers a place to discuss your work you can start anytime, right? Why wait? The server doesn't even have to be purely about your webcomic. It can be a place to post your sketches and concept art, links to other places you hang, or fanart for stories you appreciate.
If I were you I'd just make it, populate it with some nice channels, invite your readers there and see what happens. If you have webcomic-related materials, share them there. If you want to make it fun, make a quiz online for readers to complete to see what characters they are, or other things that are interactive and interesting.But yeah. Can't hurt to try can it?