Hi!
I'm no expert, but my youngest, who is 11 months old, went for a while of having the ol' 1h20 nap. For me, if she was happy during her A time and fell asleep relatively "quickly" and without getting upset, I was ok with it (this was also after about 2 months of 35 min naps, so maybe I was just overly excited! haha). I experimented with her A times as well, adjusting by about 10min either way depending on her mood; each adjustment I kept for about 3 days to see if it worked.
As for the one nap, when I moved my oldest to one nap (yes, I had to move her, she was not going to do it willingly - that girl would have napped her life away if given the chance!) we went from 1x1hr & 1x1.5hr naps to a whopping 1x2.5/3hr nap; that stuck around for a couple of months, and then as she got older, it naturally shortened; when she turned 2yrs, we capped it at 1.5hrs (again, would nap all day), and at 2.5yrs capped it at 1hr. Now she's 3, and she naps maybe two or three times a week, sometimes for a full hour, other times for 30min because we set her end-of-nap-time to protect bedtime. Anyway, that's just my experience; and other friends have noted that on 1 nap, it tends to be longer than when they were on 2 naps.
Good luck!