I'm really sorry if this has been asked before, but i'm in a bit of a problem..

I was just going to sub normally monthly and i was sure that i will get the 90 days needed for the mount but, I've been playing with my friends on Zalera and my MC just hit lvl 30 and i was awarded free 15 days of game time, now i know that free time doesn't count and the mog station won't let me add more time till the current one expires, i currently have 21 days left including the 15 and i won't make it to 90 days before the end of September, what do i do in this case? XD

I am currently using Entry, should i change to standard and sub for 90 days? or wait till September and add just 60 days? i don't want to stack days ....