Pretty sure I’ve seen topics opened after that which, once solved, closed 3 hrs after the last reply, which in one case was immediately. However I haven’t been paying attention in the last few days, so 
.
The timer starts at the time of the last reply. IMO it should start when the thread is solved and be reset when a new reply is created.
And that’s basically what it does.
Seems fixed now, hopefully it will not reset again on the next update of discourse.
That’s, what updates are for 
Well it starts when the thread is marked solved, but the start value is from the last reply. So if the last reply is older than the time period, then the thread is immediately locked.
If memory serves, it happened at least once about a week ago.
Which makes perfect sense. Sometimes Quite often the original poster abandons the thread without marking a solution, even though the issue has been solved — it’s all part of the selfish/narcissistic atmosphere of the time. And then someone comes along who notices this and marks a solution, but because the thread was abandoned days earlier, it then immediately gets closed.
Threads that have not been closed are like a magnet for necro-bumpers. We regularly have to split or delete posts that are added to threads which are already months or years old, due to newbies already having discovered how to write — albeit poorly — before having learned how to read. 
Ah, but not when it’s a fresh thread, the last reply is ~3hrs old, and the OP marks it solved, then immediatly tries to ask a follow up question only to find the thread is locked.
That’s with the old settings. For new threads it is now set to two days.
It’s two days now, as agreed upon by compromise.
So, you’re saying this only now filters down to the lower decks? 
Eh 24 hours would have been more than enough. Some threads just go on and on forever without anything useful being said after they’ve been solved.
This is probably because the default timeout for those particular threads was still set to 3 hours. It all depends on when the thread was created — i.e. before or after the timer template was modified.
This is certainly true, just as some threads go on and on forever due to the original poster either being obtuse, or a help vampire, or both.
The timer is usually triggered when a solution is marked
But moderators & community assistants can set timers on any open topic
The ‘Close Temporarily’ timer is the only one I recall having been used by moderators in the past
Windmills of your Mind - Dusty Springfield
Like a circle in a spiral
Like a wheel within a wheel
Never ending or beginning
On an ever-spinning reel…
Well, even 48 hours is fine, when considerting the topic can be renewed in a new thread, if needed. Of course, by that argument, 3 hours is also fine. 
We account for the “internationality” (is this even a word?) of the forum. Between USA and Australia there are about 15-20 hours of “lost” time (in sleeping/working), so i think the minimum for everybody to have a fair chance globally is 2 days as it is now.
Topic is marked as solved. It’s done. Who cares where’s what. Let’s see how long this one will drag on.
This is true, but there is sometimes good reason to allow additional comments.
if there are additional, relevant details which improve the resource - and sometimes comments about the solution accepted.
if there are interesting alternative solutions.
So extending the clock hopefully serves to improve the coffin and give more time for good people to polish the nails. I believe there are currently over 124,000 nails - but it’s an extremely large coffin and so there’s no need to panic just yet.
…and it seems to be 3 hours again
Two days now; for new threads, apparently.