absences under ILR

I have read the gov. information on absences whilst under ILR, but it is not specific enough. My wife's daughter wants to study in Portugal and we would like to accompany her. We would maintain a property in the UK and come back every so often for a few weeks or maybe months. When the gov. say two years maximum, is that continuous or could one 'renew' the two year limit by coming back for a month or two each year? The course in Portugal lasts three years.

OK, just read a recent post on similar issue, now answered!!