No time limit. If you're trying to join on an Apple device, you may need to adjust some settings before you can join.
1. Sign in to Discord on desktop and navigate to your User Settings. You can find your User Settings by clicking the gear icon in the bottom left corner of the app.
2. In the User Settings menu, click on Privacy & Safety.
3. Find “Allow access to NSFW content on iOS” and click the toggle. This will let you view NSFW servers you are already a member of from your iOS device.