Uptime is the total number of seconds that the computer has been up or user logged on or whatever.
There are 86400 seconds in a day… from there it’s an easy math problem 
If you have 200644.28 as an uptime take that number and divide by 86400 and you’ll have your answer…
2.322… days or rounded 2.3 days… as for the .3 well again a simple math problem…
that’s bascially 1/3 of a day… so I"m going with 2 days, 8 hours give or take… 
Are you looking for a way to show that?
if so you could possibly do something like this:
[php]
$uptime = shell_exec(“cut -d. -f1 /proc/uptime”);
$days = floor($uptime/60/60/24);
$hours = $uptime/60/60%24;
$mins = $uptime/60%60;
$secs = $uptime%60;
echo “up $days days $hours hours $mins minutes and $secs seconds”;
[/php]
Some of the other guys are way better at this then I am but this is just a suggestion…