Hmmm. I think even if he does 1hr nap, 5pm is a little on the early side - you'd need minimum 12hr night or he'll be up before the birds. In our house we always had a rule that BT would be 6pm at the earliest - we couldn't practically do it any earlier.
I actually think if you want to see a consistently later WU his nap needs to go back to around 12.30pm start, but with such an early WU it will be very hard to achieve. I think your best bet may be to stick consistently with nap at 11am for a week, (hope he does 2hrs) & BT at 6pm. Then push it all on 15mins so nap 11.15am, and assuming 2hr nap, BT at 6.15pm (a little earlier if he short naps). And so on, 15mins later each week til nap is starting at 12-12.30ish. It will be very tough going, but it is kind of a set nap so it gives consistency, and the early bedtimes should help limit OT, and by pushing the nap later (& therefore BT later) you will break the cycle of early waking. I did this at 15/16 months & it was horrendously difficult & DS got very very OT but it helped tremendously & we had 2 months of blissful 7am WU, 12.30-2.30 nap & 7.30 BT before the 18 month sleep regression hit us hard!
