Last time we me we decided that at one meeting a month we would consider doing things slightly differently. This could include listening to a dharma talk "on tape" or perhaps reading an article, possibly from the journal. In order to fit this in we would need to change the meditation sittings slightly so we do one longer one (perhaps 30 mins), rather than two 20 minute ones.
We would take it in turns to consider what extra to do (if the person that month wants this).
If a new person was coming to the group for the first time we would stick to the normal routine including 2 twenty minute sittings.