Many thanks to both of you for your kind replies and swift assistance!

Ultimately, I was able to use what @maroon posted to modify the uptime script, and was able to successfully output in the format I wanted after a fair bit of trial and error.

Previous output, using uptime snippet from HM2K's moo.mrc v3.17 system stats script:
Code:
Current Uptime: 1day 1hr 38mins 4secs - Time To Beat: 18wks 3days 15hrs 33mins 29secs

on *:connect: up x
alias up { ;uptime v0.4
  $iif($timer(up) == $null,.timerup 0 60 up x)
  if (($uptime(system,3) >= %up) || (%up == $null)) set %up $uptime(system,3)
  $iif($1 == x,halt,$iif($chan,msg $chan,$iif($active == Status Window,echo,say)) $+(Windows,$OS) Uptime: $uptime(system,1) Best: $duration(%up))
}

Modified output, including minor cosmetic changes:
Code:
Current Uptime: 1day 2hrs 22mins 35secs - Time To Beat: 129days 15hrs 33mins 29secs

on *:connect: up x
alias up { ;uptime v0.4
  $iif($timer(up) == $null,.timerup 0 60 up x) 
  if (($uptime(system,3) >= %up) || (%up == $null)) set %up $uptime(system,3) 
  $iif($1 == x,halt,$iif($chan,msg $chan,$iif($active == Status Window,echo,say))) $+(4Current) Uptime: $uptime(system,1) 4Time To Beat: $iif($int($calc(%up / 86400)),$v1 $+ days) $duration($calc(%up % 86400))
}

Again, thanks to both of you for your input, and thank you for responding so quickly. Cheers!