i suggest you to call them once your baby reach 1yr old and ask them how many babies are on the waiting list in front of you so you get an idea of how long to wait.
My son attend the HG playgroup for few mths, although the waiting list is quite long but still have chance coz the schoolmates change every mth, at least 10%. Or u can call & ask
yes, better call. my son is studying PG there too. As i know the school wants to control no. of seats per class (around 8) for better quality, so actually seats will be available when 1) there are kids over 2yrs; 2) quitted; 3) new semester