my mum who is a chiropodist says it all depends how long it usually takes your nails to grow!
apparently a toe nail takes up to 6 months.. but a finger nail should take less..
I cut my fingernails aprroximately every 2 weeks. They grow approximately 3mm during this time. Therefore if your fingernail length is 18mm it would take 6 x 2 = 12 weeks.