Definition of 'recent' for messages

Hi all,
I'm looking for the option to determine the opened and closed groups in the 
email panel. There are three options: 'always open', 'always closed' and 'only 
open for recent messages'. Also during searches there is an option 'status = 
recent'.

Is recent two days, 24 hours, one week? Is there an option to set this recent 
status?

Thanks in advance,
Jurian