Changing what 'Recent' means

From PluginWiki

Decreasing the limits

By default, the plugin considers messages within the last 31 days to be recent. That means:

• They count towards the member's message summary.
• They're available for crosspost checking.
• They are considered for duplicate checking.
• They cause the member to be shown as Active in.

You can lower - but not increase - these limits from Features -> More Advanced Options:

Changing these limits will take effect next time you refresh a page.

Using Calendar Months

Normally it'll tell you about messages within the last however many days, which is normally what you should use. 

But you can also tell it to use calendar months, by ticking the checkbox. That means that it will just tell you about messages within this month, i.e. all counts are reset to 0 on the 1st of the month, so you won't see anything from the previous month (even if it was only yesterday). 

Increasing the 31-day limit

It's not recommended that you increase the limit beyond 31 days - doing so means it takes longer to load and process pages, will store more data on your machine, and be a bit more likely to go wrong and reduce your machine to a heap of smouldering rubble.

• NOTE you can also decrease the number of days using this technique if your group doesn't need to check this frequently...

But if you really really want to, then you can do so by changing the Firefox preference directly. Information on how to do this is here, and the preference you should change is extensions.modplugin.recentspan.

Once you've done this, you'll need to do Check Cache from the Debug Options tab before it will take effect.