It only takes a few days to the hormones to stop working i.e you will become fertile. I had the implant removed in May but when straight onto the pill as wasnt ready for a baby. Came off the pill 3 weeks ago as i am now trying for my first! When i had the implant taken out though the doc said it takes around 2-4 days for the hormones to settle down again. Cant pinpoint the exact day you'll start ovulating but BD obsessively and you cant go wrong!
Im 35 aswell and had my implant removed in august to TTC #4 (this will def be my last!) i ovulated 3 weeks later and AF followed 2weeks after that, in those 5 weeks i was extremly confused as i had constant cramps & sore boobs, did countless OPKs and HPTs (very frustrating), ive just ovulated for the 2nd time since removal so hoping my body is settling down & this will be my lucky month, doc told me you can POSSIBLY become fertile within 24hrs of removal but it could take a couple of mths before you return to a normal cycle, good luck with TTC