From
Changelog:
When a grouped chat contains unread messages, Messenger Plus! automatically switches chat windows after some delay if the group is not currently active. This delay can be changed with the "GroupAutoSwitchDelay" registry setting.
You change this manually:
HKCU\Software\Patchou\MsgPlus2\your@email.com\Preferences GroupAutoSwitchDelay dword 15000
This delay, in milliseconds, is the timeout used by the tabbed chat feature before a chat window with unread messages is brought to front.
Or with
MsgPlus! Tweak 
(MsgPlus! Tweak is a program wich can change those advanced settings for you, without you having to go into the windows registry yourself)
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