My record number of finds is 50 in a day which I did last month (on 20 April 2015). That day I did the 40 puzzles of the FF40 series in Oxfordshire, and then added 10 more to make a total of 50 puzzles. My statistics are visible for checking but I'll add a screen shot of the relevant line anyway.
It took me about ten minutes to find the cache. I was surprised that no muggles walked past in all that time (it being 5pm on Saturday). Nothing seemed to match the hint at all but then I suddenly spotted it. The cache was a few feet away from the hint item (where there was a little pile of stickoflage) so I replaced it there.
I'd just finished all this when two female joggers came past. So perfect timing.