yes the longer you can wait to purchase the better as you get to see how the horse is developing
and in fairness you should pay for the months of training already accrued
but that is assuming the horse you are interested in has shares available from the stable ,
if 100% of shares are sold than you would have to buy from current owners who might want to sell and at what price
for example roy hill is all sold out , so if you want shares a current owner would have to sell them to you