I am trying to remember when my little boy changed to one nap a day, but I think it was about 13 months.
Does your baby have trouble falling asleep for his naps, too? If so, I would definitely cut it down to one. I remember cutting it down to one when falling asleep would take my boy so long it was driving me crazy and I wanted to reduce the agony for both of us by having less falling asleep times lol.
My boy was never a good sleeper and always needed me to be with him to fall asleep, so I think I haven’t seen so much of a difference in terms of him not settling on his own. However, I am aware that separation anxiety can really kick in around your babies age and later, so it might be that? If so, I think the best remedy is patience and just wait until he feels more secure again, which I don’t think you can rush, it’s just part of their development. With time and doing what you know works for him, he will surely get back to his normal routine of falling asleep and settling quickly.
In terms of bedtime I think there are different opinions if an earlier or later bed time is better. My boy never went to bed before 8pm and often 8:30pm (it just fits our home schedule better), but as a pay off usually sleeps until 7am or longer in the morning! He is 2.5 though. I think when he was younger he would wake up earlier, but never before 6am!
I would just give it a go to go to one nap and perhaps make that longer if baby wants to sleep longer and do it as late as possible in the morning/early afternoon and maybe keep bedtime at 7/7:30m if possible. If you feel your baby is overtired after a week, you can always go back to two naps again for a while or change bedtime!
Apart from that, just do what causes you and baby the least stress (it sometimes takes a while to figure out), i.e. stay with baby for a little longer to fall asleep if it means less crying and just use it as relax time or read something if possible and be less stressed about the changes and soon enough I am sure it will all settle itself. Probably just a developmental phase!