Although there is one month between payments, if you pay by instalments, there are only 5 instalments, i.e. at the end of September, October, November, December and January so each one is one fifth of the total. Note that the November payment is due on the 29th because the 30th is a Saturday and so not a working day. The electronic payment code is the same for all five instalments or for a single payment.
The reduction depends on the objective value of the property. A 27% reduction applies to properties with an objective value up to €70,000.