Hi there
If you cap a nap, then you need to ask yourself-for what reason and for how long. I understand that capping is needed sometimes when you get to the 2-1, but I wouldn't cap more than 45 minutes. A LO isn't going to survive very long on 30 minutes, especially if they are NWing, EWing and short napping.
(on a side note and as a general 'rule', I wouldn't let the morning nap go past 11 am, but that's not really going to apply to this age group
).
Why cap the morning? Is it to ensure a Pm nap? If so, then I would first try moving the morning nap earlier for 4-5 days (yup, I know this is counter intuative, but sometimes going to 8:30 instead of 9 works for some reason), then I would try capping the morning nap at an hour, 45 minutes at the most for a week, then I would try moving the pm nap to 1:30 and then if your LO is still refusing a nap for 2 weeks straight, then I would move to 1 nap.
Claire if your LO is taking a 2 good naps, I would still keep bedtime to about 4 hours after they wake up. Any longer and they're going to get more OT, especially if they haven't been sleeping that well to begin with.