To be honest it took about 3 months to get my ds#1 to 1 nap & I am working on it taking about the same with ds#2.
today my ds#2 woke at 5.15am & I spent until 6.55 to get him back off again... he then slept another 45mins... I always work until 6.30 to get him back off no matter what, but this morning he was showing he was tired so I gave until 7am... now I will try every morning until 7am, even though it is hard with a todder running around from about 6.40am.
What I am doing is cutting the first nap short... no more than 45mins, soon to be no more than 30, if that means I have to bring the 2nd forward slightly & bedtime that is ok, cos better than an overtired baby, although what I tend to do is compensate, by a longer bath & a trip in the stroller so bedtime remains the same, unless he is super cranky, as I know if he is overtired at bedtime, not only do I get nightwaking, BUT also an early start. 7.10pm is the absolute latest I can get ds#2 to bed & possibly avoid them, but 6.55/7pm is a better time.
My rule of thump is to work out the average sleep needs for age (at 12mo it is about 14 hours) & if night sleep + day doesn't equal that, then I put to bed a bit earlier. So say today, 5.15 + 45 =6am... so for a bedtime at 7pm, he needs about 3 hours of day sleep, (total 10 hours awake time) so if he gets 2.5 or less then I will bring his bedtime earlier.
I would delay the first nap by 10mins, then keep it at 45mins max... he has shown he is capable of 4 hours awake time as he si doing 5.30-9.30, so I'd move it later by 10mins every 3-4 days & then always make sure he is awake giving 3.5- 4 hours until the next nap, unless he is overly grumpy then maybe earlier.
For reference our day (maybe 3-4 days a week we get it right)
6.30 wakeup & bf
7am breakfast
lots of active play
9.30am Nap - up by 10.30 at latest
snack on waking
Out to an activity
12.30/1pm Lunch
1.30/2pm Nap
3.30/4pm bf on waking
lots of active play
5.30/6pm Dinner
6.30pm bath
6.50 bf & bed
As I have a toddler to work with it doesn't always go to plan & usually those are the days we have the early starts the next day.