I can't find it on the GUI pages.
My attempts to ssh and telnet to the RB all timeout without any response

One of the first thing I did find when googling RotuerOS uptime.
https://www.youtube.com/watch?v=qWlHOwD9gwg

I have deduced his switch is one RB260GSP and probably still have version 1.14
Like all the others (rightly) unanswered, or (rightly) answered like "search first",
do not provide any clue of what machine is or what RouterOS (SwOS in this case) is installed.
Very bad habit.

His switch have SwOS and ask where see uptime on GUI not WinBox.
WinBox can not control SwOS.

Title of the thread is "How do I find the uptime of my router?" and "RB"is mention.
So OP should post what software/hardware and version he has.

P.S.:

>>>My attempts to ssh and telnet to the RB all timeout without any response

And SwOS do not have SSH and neither Telnet...

How do you know its a switch OS?
Telnet/SSH may be blocked.

How do you know its a switch OS?
Telnet/SSH may be blocked.

Nice question :))

As I write before:
>>>I have deduced his switch is one RB260GSP and probably still have version 1.14
viewtopic.php?f=2&t=122267&p=601428

I doubt than I have the courage to upgrade a 4000km (~2500miles) away switch with possibility of failure of any type...

He may have more than on device :)

He may have more than on device :)

We discover it in 4 years ...