Nap has been shortened?

I have recently moved nap time back 30 mins (they were going down at 12 but now 12:30) but I am finding they are waking early (1.5 hrs instead of 2). Could they just still be on the same internal schedule? I am leaving them the last half hour in their cribs/cots to hopefully retrain.

Moved nap because I don't have any am nappers anymore and this allows us more time at the parks in the morning and makes for a smoother afternoon (just wake up, snack, play and pick up). Plus I just took on a half day girl and she is getting picked up at 12pm so I wanted to have 30 mins more to settle the rest after she leaves.

I think it is probably just a matter of retraining them. Give them some time to adjust and keep doing what you are doing by leaving them the last half hour and see how it goes over the next few weeks

I have a little boy who falls asleep at the table if nap time is later than 12.15 (lol). Like brightsparks says it will probably take a few weeks to adjust, fingers crossed it happens sooner rather than later