I’m wondering if there are any settings or plugins that could help support a user’s mental health? For example we have a very active community and sometimes find that they post a lot. Wanted to look into whether it was possible to allow them to set their own limits on how long they can spend on a Discourse forum?
I realise users could just stop, but I think that this might be a useful option for those who find it hard to stop replying to notifications.
For each Discourse site I use, I set up my Notification preferences (/my/preferences/notifications) to the following:
Being liked is nice, being notified is a bit distracting.
Even when I’m active on a site, I want bounds on how much I’m being drawn to it.
If the site uses Assignments, setting the frequency of the reminder messages is useful.
Another panel of settings to check is (/my/preferences/emails), as that will greatly reduce received email:
I hope those provide some assistance. 
Maybe something like Take a break! Theme component is what you are looking for. But I don’t think users can choose the time after the reminder is shown
i’ve set members to lower trust levels temporarily at their request for this reason.
