At 3 mine was no longer napping, he did (and still does) a 12hr night.
Before dropping the nap (2.5) he did a steady 2hr nap and 10hr night. We had a few months transition where he could not shorten or skip the nap but nights went silly short, down to 9hrs.
Lots of people do shorten the nap and the night increases as a result, for some though (like mine) they need the sleep spread across day and night to stay fully rested and once they can manage it they drop the nap cold turkey.
The thing with the gro-clock, if you use it correctly and consistently it really can help to increase the night sleep if they need more sleep (ie waking too early and then tired and grumpy in the day) but it can take a lot of effort to make the gro-clock work and the routine needs to be suitable - it won't just make a LO sleep if they are not tired.
I would shift the whole day so nap comes later, later BT and later WU.