How is it that some people have managed to advertise their upcoming gold critter when the vase hasn't been at the minimum 12 hour wait ....I remember going to advertise when i was doing them before, as didn't think about that side of it and it didn't let me as although i may have had the plant/s in ready for that critter, i wasn't officially attracting a gold one....

I have always found that you can advertise before your vase is ready, I don't think the programming is set up to know if you are attracting or not based on the timing of the vase as it clearly wasn't factored in when making this change.  However I never advertise unless I am actually attracting the gold wildlife. 
With the new programming you can no longer advertise unless you're set up correctly and this was abused so many times that this change came about but people will always do this if they can so it always pays to check if they actually are ready regarding the vases.

There is a note that is set as follows when you go to the guide for a specific gold critter:-

Important: Gold Wildlife can be advertised as soon as the Bouquet to attract them is completed. However, the Bouquet needs to have been completed for at least 12 hours before the Gold Wildlife will visit, so remember to check the time on the Bouquet!

As Paula has said above, technically if you have the gold vase in the garden and the correct food and attractants, then you are set for the critter - timing on the vase is probably just one criteria too far to add for the programming so the note is added in to the information for each gold critter.

Well it wasn't that long ago that i was doing them before this new lot and i advertised as i said and it wouldn't let me so i just find it strange that you can now, that's all. No biggie, just weird :)

It's been like it pretty much since the beginning, there are threads moaning about it from over two years ago :)