Skype for Business

To change settings for:
Show me as Inactive when my computer has been idle for this many minutes:
Change my status from Inactive to Away after this many minutes:
when they are greyed out on a PC.

I TAKE NO LIABILITY IF YOU MESS UP YOUR MACHINE

For Show me as Inactive when my computer has been idle for this many minutes:
Go to registry (by searching for program called REGEDIT) > Find > IdleThreshold
(there can be multiple keys, but the path I want in Win7 is HKEY_USERS\[code]\Software\Microsoft\Office\[version]\Lync which can be seen at the bottom status bar of the Registry Editor)
Change value data as Hexadecimal between 5 and 168 (the latter data number in brackets represents minutes used by SFB).

For Change my status from Inactive to Away after this many minutes:
The key is kept in the same path (as in above instructions). The key is called: AwayThreshold
Like before, change value between 5 and 168.

Restart your computer to make sure the settings take affect.
Start up Skype for Business to check the settings in Tools > Options > Status

Note 1: There are lots of other conditions that causes SFB to go into Away mode, such as Windows going idle.
To prevent Windows screen saver (on Windows 7), try Control Panel > Personalization > Screen Saver (botton right) > Wait 9999 minutes.
Also (may be try) Power Settings / Options > Turn Off Display > Never

Note 2: Administrator can change the values by routine scripting, you could probably counteract with your update script.

As of: 29 August 2018 / Windows 7 / Office 365 / PC.