I have natural cycles that are short (24-26 days) all my life - used to be 24 day cycles almost exactly years ago. Dr. C told me too that I O'd early and that's not good (didn't want to offend him so I didn't drive home the fact I conceived my DD on 24 "exact" day cycles - and had a positive pregnancy test by day 21. I figured I O'd around day 10 - maybe 11 (as I always have at least a 13 day LP and sometimes 14 days). Maybe ER changes things about egg quality if too early, but I found the E2 priming lets me go too long like ER on day 13, 14, or 15 - which is unnatural for me. So guess it depends on your natural O. I just think the RE's should mirror your natural cycle length - what you had without high FSH. So if day 12 is your natural O day, then I would say try to mirror that. I could be wrong and am not an expert but it makes sense to me to mirror nature!
Now, I drive home the fact to all docs and RE's that my cycle have been and always will be short b/c that's what they were at 20+ years old. I had one local RE say... are you sure. I did not go into it with him. Sigh!