how can you break down the 0x25 packet to get the server uptime?
SID_PING (0x25) doesn't include the server's uptime anymore. It's now just a random value.
Compatibility for older clients?
SID_PING has always included a DWORD.
Blizzard games didn't care about the value, they just replied with the same value to Battle.net.
The Battle.net server could use any value here, and it used GetTickCount(), which returns the server's uptime.
Bot developers found out about this and abused this (to show the uptime). This was also abused to spoof lag.
Blizzard didn't want the uptime to be known, and today SID_PING sends a random value as Spht said - and lag spoofing is no longer possible either.
Blizzard games still don't care about the value, they still just reply with the same value.
Any questions? :)