How old is he?
With hindsight, I recognize that my daughter's waking in the middle of a nap was almost always under-tired (with the exception of the first few months, when it was definitely undertired). In addition, EW for her is also a sign that she's needs a later nap. So it may be that he just needs more awake time.
My DD is LSN, which I actually didn't realize for quite a while. She started the transition to one nap at around 7 months. Transition took till almost 13 months. We started with one nap at 11:30, and then to avoid overtired during the transition, I would often give her a catnap around 5pm (capping at 30-45 minutes), and APOP if I needed to. Once that became too difficult to manage, I knew she was ready for only 1 nap, and we moved it to noon. Once we were on 1 nap at noon, we were pushing it back by 15 minutes every 1-2 weeks. Then around 16 months, she was napping consistently at 1pm for several months. At 22 months, she's now napping at 2pm for 2 hours most of the time, but sleeping for 1.5 hours every few days, so I think I'll see the 1-0 happen in the next 2-4 months. We're on 13 hour day, waking at 7am, bedtime at 8pm.
So generally, to answer your question, I found moving the nap out happened very quickly and very often.
I hope that's helpful!