I think it depends on many things .. by law they have to give a decision in 90 days so you cant complain if it will take that long time.
First of all it depends on your passport from which country you are holding yours? if from country that doesnt require visa entry I think working days for your visa would take less time than 90 days. also make sure you giving them all required papers , double check the required papers and you can find that online , when you go there make sure they got all your papers and ask them if there is any missing paper ,take a recite ,and if u dont speak the language company one who speaks it to avoid any misunderstanding.
I hope i helped even if it was a little bit