When I weaned my first son at 12 months, I believe it took me nearly a year before I could no longer express any milk! It all depends on your body I guess. My family calls me the "Dairy Queen" because I seem to have a never ending supply of milk LOL
I know weaning is a personal decision and you're probably making the best possible choice for you, your child, your family... but, when my oldest son was 1, I was told flat out by his pediatrician that I had to stop nursing him (back then, it was only recommended to nurse for 6 months, so I was quite the rebel in going "so long") - I regretted it SO much!!! It was the worst parenting choice I may have ever made (or close to it). I vowed to never again be pressured into weaning (as neither myself nor my son was truly ready to wean at that point). I nursed my second son until just befor his 3rd birthday and am just over 2 years and still going strong with my 3rd son. If you're feeling pressured by anyone to stop, I'd just like to encourage you to carefully evaluate how you and your son feel about your nursing relationship and know that the World Health Organization recommends a minimum - yes a MINIMUM - of TWO years!! Long term nursing is nothing to be ashamed of and carries extraordinary benefits for your child.
Sorry if you feel I am being preachy, but I'd never want another mom & baby to suffer like I feel my son and I did all those years ago!